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Research on Characteristics of Fiber Optic Sensors for Anthropomorphous Robots
Available online at www.sciencedirect.com
ScienceDirect Procedia Engineering 176 (2017) 128 – 136
Dynamics and Vibroacoustics of Machines (DVM2016)
Research on characteristics of fiber optic sensors for anthropomorphous robots Sergey A. Matyunin* Samara National Research University, Moskovskoe shosse 34, Samara, 443086, Russian Federation
Abstract Structure, operating principle, theoretical provisions, experimental characteristics of fiber optic sensors for control of a bending in phalanxes of the anthropomorphous robot fingers, as well as principle of compensation for cross impact of adjacent measuring channels are considered. Linearization algorithm of positional characteristic of a sensor is given. The use of compensation algorithms of the cross impact and the linearization of the positional characteristic of sensing element offered to reduce nonlinearity of the sensor positional characteristic to 1% and to reduce the cross impact of different measuring channels to minus 20 dB, which is confirmed by experimental studies. Results of the experimental studies revealed that even without application of special temperature correction methods, the sensors used possess sufficiently high stability. Their phalanx temperature coefficient does not exceed 0,08%/°C. Assessment of high-speed performance of system, taking into account computing opportunities of the electronic transceiver is carried out. Technical characteristics of sensor prototypes and the electronic transceiver of fiber optical system are given. © Published by Elsevier Ltd. Ltd. This is an open access article under the CC BY-NC-ND license © 2017 2016The TheAuthors. Authors. Published by Elsevier (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of organizing committee of the Dynamics and Vibroacoustics of Machines (DVM2016). Peer-review under responsibility of the organizing committee of the international conference on Dynamics and Vibroacoustics of Machines Keywords: System of fiber optic sensors; angular movements measuring; phalanxes of anthropomorphous robot fingers; compensation of cross impact of different measuring channels; algorithm of positional characteristic linearization; electronic transceiver structure.
1. General characteristics and problems of sensor creation for anthropomorphous robots In modern robotic platforms of land, air, space basing, and in anthropomorphous robots, “electric” measuring transducers (sensors) are generally used with output electric signal in a digital and analog format [1-3]. Such sensors
* Corresponding author. Tel.: +7-927-717-10-68; E-mail address: [email protected]
1877-7058 © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of the international conference on Dynamics and Vibroacoustics of Machines
doi:10.1016/j.proeng.2017.02.280
Sergey A. Matyunin / Procedia Engineering 176 (2017) 128 – 136
possess high metrological characteristics, which allow integrating them by relatively simple means into general communication line with central processor. On the other hand, a particularity of “electric” sensors is their relatively large dimensions and a high sensitivity to external electromagnetic fields, as well, as creation of own electromagnetic field that is not always desirable. High sensitivity to the external electromagnetic fields and to ionizing radiation imposes restrictions and creates certain problems in their use, for example, in robots for repairing space international stations in conditions of near-earth space. This is particularly evident in development of manipulator sensors and smart skin of the anthropomorphous robots. At the same time, implementation of spatial position sensors in manipulators, captures and tactile sensors of the anthropomorphous robots based on principles of creation fiber-optic measuring systems [3, 7 -11] allows reducing overall dimensions of sensing elements by 3-5 times, placing electronic transceivers for sensors out in a remote case with special protection, in which the central processor of the robot can be placed connecting them to each other via optical fiber that is insensitive to an electromagnetic impulse and ionizing radiation. The overall dimensions of the sensing element of the sensor and the communication fiber line are mainly defined by optical fiber dimensions (0,30,9 mm in diameter). Of particular interest are fiber-optic sensors (FOS) with a closed optical channel, as fundamentally “nonelectrical” and non-subject to contamination of the optical channel. For autonomous robots, operator-controlled manipulators and exoskeletons, the most important problem is obtaining a reliable information about the state (position) of the executive power bodies and about force-torque perceptions transmitted to the operator. Such measuring systems can be implemented on the basis of fiber-optic position sensors (displacement) [6 - 12]. By the time, a set of FOS for movements based on conversion to amplitude and phase shift keying of radiation and to shift of a spectral characteristic in optical radiation, etc. [4-19] has been developed. Presently, a lot of displacement FOS was developed based on the transformation to amplitude and phase modulation of radiation, shifting the spectral characteristics of optical radiation, etc. [5-13, 17]. At the same time, despite all prospects of the FOS, their ubiquity is not observed. This is due to high cost of equipment (mainly the cost of electronic transceiver), lack of unification, and a small assortment of the FOS produced. Thus, the relevance of works on creation of new FOS is determined by their major advantages over the “electric” sensors and the incompleteness of research in the field of creation of specialized FOS with different physical values for specific tasks of controlling robotic mobile platforms. Purpose of researches is development and research of FOS system for angular movements measuring of phalanxes of the anthropomorphous robot fingers. 2. Principle of operation Discussed FOS measuring systems (MS) of phalanxes angular movements of the anthropomorphous robot fingers are based on modulation of bending losses in optical fiber during its deformation. The MS (Fig. 1) consists of electronic transceiver (ET) placed remotely from the FOS, fiber optic sensors (FOS1-FOS3) and fiber-optic communication lines (FOCL) connecting the FOS1-FOS3 with the ET. The structure of the ET includes: power module (PM), reference-voltage source (RVS), laser diode (LD) connected to a power source (LDPS) with a circuit of optical radiation stabilization, optical splitter (OS) with a number of output channels according to the number of robot fingers phalanxes distributing optical radiation on the FOS1-FOS3, inverse optical splitters (IOS1- IOS3), for example, made in the form of circulators separating FOS1FOS3 signals from LD signal. The FOS-FOS3 are located in the joints of the robot fingers phalanxes. FOS1-FOS3 optical signals via the corresponding IOS1-IOS3 are transmitted to photodetectors (PD1-PD3), which is then digitized and converted in the analog-to-digital converter (ADC) and microprocessor computing device (MCD). The MCD is connected to the onboard control system (OCS). Wiring scheme of a sensitive optical fiber in one of fingers of the robot is given in Fig. 2. Properly, sensitive elements of the FOS1-FOS3 represent segments of optical fiber with multi-layer metallized coating in a polymer shell with 0.3-0.9 mm diameter. When the phalanxes of the robot finger bend, corresponding segments of the
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sensitive optical fiber is deformed (bending) and, as a result, a part of the optical radiation is output to the optical fiber cladding and is absorbed by it, thus changing the optical transmittance of radiation. The FOS sensitivity calculation is reduced to the calculation of the radiation losses due to bending of the optical fiber. However, in this case, it is necessary to distinguish “useful information” regarding optical radiation modulation and “interfering information” regarding modulation. For example, FOS1 signal (Fig. 2) is not influenced by the deformation of the optical fiber of phalanxes 2–3 (but the FOS1 signal is influenced by the deformation of the optical fiber in its hand-to-phalanxes articulation 1, not shown in Fig. 2). FOS2 signal is influenced by the deformation of its optical fiber in the phalanx-to-hand articulation 1. FOS3 signal is influenced by the deformation of its optical fiber in the phalanx 1-to-phalanx 2 articulation. The bending of the optical fiber in the hand influences all of the FOS1-FOS3 signals.
Fig 1. Structure scheme of the SM.
Fig. 2. The wiring diagram of sensitive optical fiber.
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Deformation of sensitive optical fiber is characterized by radii of local fiber bendings within its laying inside the robot’s hand. As light travels along the fiber in the form of modes, attenuation of each of these modes depends essentially on the fiber bending radius [15-17]. In the sensor considered, the bending shape of the optical fiber in the FOS1-FOS3 is determined by the method of its mounting on the phalanxes of the robot (Fig. 3). Option 1. Motionless fixing of the optical fiber on axis (pulley) of a finger phalanx (point b, Fig. 3) with movable fixing in points a, c of phalanxes of fingers. Option 2. Motionless fixing of the optical fiber in points a, c of finger phalanx with movable fixing in point b. The first option of fixing practically results in that finger phalanx rotation causes the optic fiber to slip at the fixing points a, c due to elongation/shortening of the fiber. In addition, when the phalanxes turn on the angle φ, a double “fiber fracture” is observed at the point b. It is obvious, that in order to avoid optical fiber breakage, its excess/shortage on the right and on left of the b point has to be compensated by an additional loop of the optical fiber in the phalanxes of the fingers. The second option of fixing is more preferable, as there is no movement of the optical fiber in phalanxes of fingers, the excess/shortage of the optical fiber is compensated by radius RP alteration of the optical fiber loop.
Fig. 3. Scheme of fixing sensitive optical fiber.
In the Figure 3 the following references are accepted: Ro – pulley diameter, which forms a curve of the optical fiber bending; [0, max ] - current and maximum rotation angles of the finger phalanxes; RL , RL0 - initial (at ϕ=0) and current radius of the optical fiber loop. The current radius of the optical fiber loop is defined by expression: RL RL0 R0
. 2
(1)
The form of a bending shape of the optical fiber passing by the FOS1-FOS3 is close to circular and can be set by one radius of RP determined by points of fastening the optical fiber to the phalanxes of the fingers (Fig. 4): RP
d , sin ( / 2)
(2)
where d – distance from the optical fiber fastening point in the finger phalanxes to the axis of its rotation. Neglecting mutual transformation of modes in articulation places of radial and straight segments of the optical fiber, using ratios of modes orthogonality and assuming that modes of fiber cladding are effectively filtered by the absorbing polymeric covering, the power losses of optical radiation (curve 1, Fig. 5) are determined by the method described in [18,19]. According to [17-19] a good coincidence of theoretical and experimental results is observed. However, as results of more thorough research show, the real results are significantly different. It can be explained by a small number of
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experimental points in [17-19] for comparing theoretical and practical results (the experimental points just “missed” sections with sharp change character of power losses curve), and by neglecting the polarizing beats occurring due to polarization of radiation in fiber at its bending and interference.
Fig. 4. The bending shape of the optical fiber passing FOS1-FOS3
In Figure 5, curve 2 (a selection of 20 points is given) represents character of power losses curve (experimental values). It may be well observed that in section ϕ1-ϕ2 not only the sharp deviation of an experimental curve from theoretical one is observed, but also, there is an ambiguity in measurement of signal losses value of the FOS. At the same time, by selecting for operation the sections of the curve, where the ambiguity of sensor measurements is not observed, it is possible to approximate with an adequate accuracy the dependence of the FOS signal losses on the linear relation (Fig. 6).
Fig. 5. The dependence of optical losses at bending of sensitive optical fiber: 1 – theoretical losses not accounting polarizing beats; 2 – experimental results of losses.
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Fig. 6. The dependence of optical losses at bending of sensitive optical fiber in relative units with linear approximation.
Considering the observations above, the expressions for signals Y1, Y2, Y3 of corresponding detectors FOS1, FOS2, FOS3 shall have the following form. For FOS1 installation segment of the bending losses curve (partial fiber losses): Y11 (1 ) [e11 f11 ( RLO RO
1 )], 2 ],
d Sin(1 / 2) d 1 1 1 Y3 (1 ) [e3 f 3 ], Sin(1 / 2) Y21 (1 ) [e21 f 21
(3)
where: eij , f i j - coefficients of linear approximation for optical fiber segment of i-phalanx and j-detector; i rotation angle of i-phalanx. For FOS2 installation segment (partial fiber losses): Y21 (2 ) [e22 f 22 ( RLO RO Y32 (2 ) [e32 f32
d Sin(2 / 2)
2 )], 2 ].
(4)
For FOS3 installation segment (partial fiber losses): Y33 (3 ) [e33 f 33 ( RLO RO
3 )]. 2
Thus, complete signals of the FOS1-FOS3 shall be as follows:
(5)
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1 )], 2 d Y2 (1 , 2 ) Y21 Y22 [e12 f 21 ] [e22 f 22 ( RLO RO 2 )], Sin(1 / 2) 2 d d Y3 (1 , 2 , 3 ) Y31 Y32 Y33 [e31 f 31 ] [e32 f 32 ] [e33 f33 ( RLO RO 3 )]. 2 Sin(1 / 2) Sin(2 / 2) Y1 (1 ) [e11 f11 ( RLO RO
(6)
Expressing ϕ1, ϕ2, ϕ3 angle values in an explicit form resulting from the corresponding Y1(ϕ1), Y2(ϕ1, ϕ2), Y3(ϕ1, ϕ2, ϕ3) dependences, it is possible to obtain Y1(ϕ1), Y2(ϕ2), Y3(ϕ3) dependences in an explicit form. 3. Experimental studies and technical specifications Experimental studies of transient response of FOS1, FOS2, FOS3 fixed on the model of a three-phalanx hand of anthropomorphous AP600 robot (Fig. 7) were conducted. The main results of experimental studies are given in Fig. 5-6 and in Table 1.
Fig. 7. The FOS fixed on the hand of the anthropomorphous AP600 robot, the communication line and the ET. Table 1. Technical specification of FOS and ET. Object
Basic characteristics
FOS
1.Diameter, mm
0,9
2.Length of the connecting optical fiber cable up to, m
10
3.Measured rotation angle of phalanx of finger, degrees
from 0 to 60
4.Resolution capability, binary digit bit 5.Nonlinearity of the position characteristic, % 6.Reduced temperature coefficient, %/°C ET
Value
1.Number of measuring channels 2.Dimensions, mm
10 1 0,08 8 135х85х40
3.Power supply voltage, V
5
4.Current consumption, A
0,35
5.Output signal
SPI
6.Cross impact of measuring channels up to, dB 7.Sampling frequency of FOS, ms 8.Operating temperature, °C
minus 20 10 from 0 to +50
Sergey A. Matyunin / Procedia Engineering 176 (2017) 128 – 136
4. Conclusion The following results of theoretical and experimental studies were obtained: Dependence between the “beats” value of the FOS positional characteristic and the value of its deformation was revealed. The polarizing beats value is up to 5-7 dB; The compensation principle of cross impact for adjacent measuring channels was developed. The cross impact of measuring channels is reduced to minus 20 dB. The nonlinearity of the position characteristic does not exceed 1%, and the reduced temperature coefficient of the FOS does not exceed 0,08%/°C; The experimental studies of the FOS characteristics confirm the theoretical researches. Acknowledgements The work was carried out with financial support of the Ministry of Education and Science of the Russian Federation. Unique ID: Applied research and experimental work RFMEF157816X0209. References [1] Kirsanov K. The Architecture of Robotics Control Software for Heterogeneous Mobile Robots Network (2014)// 24th DAAAM International Symposium on Intelligent Manufacturing and Automation, DAAM 2013. Procedia Engineering. Vol. 69, P. 216-221. [2] Laird, J. E., Wray, R. E. III, Marinier, R. P. III, & Langley, P. (2009). Claims and Challenges in Evaluating Human-Level Intelligent Systems // Proceedings of the Second Conference on Artificial General Intelligence. [3] Xiaoyi Bao * and Liang Chen. Recent Progress in Distributed Fiber Optic Sensors. Sensors 2012, 12, 8601-8639; doi:10.3390/s120708601. ISSN 1424-8220. www.mdpi.com/journal/sensors. [4] Gerkey B., Vaughan R., and Howard A. The Player/Stage Project: Tools for Multi-Robot and Distributed Sensor Systems (2003)// Proceedings of the International Conference on Advanced Robotics. P. 317-323. [5] Shizhuo, Yin. Fiber Optic Sensors (2008) // Yin Shizhuo, Paul B. Ruffin, T.S.Yu. Francis. –Boca Raton, London, New York : CRC Press, Taylor & Francis Group, P. 477. [6] Nielsen, M.D. Predicting macrobending loss for large-mode area photonic crystal fibers / M.D. Nielsen, N.A. Mortensen, M. Albertsen (2004) // Optics Express. Vol.7, P. 1775–1779. [7]Yong-Lae Park, Student Member, IEEE, Seok Chang Ryu, Richard J. Black, Member, IEEE, Kelvin K. Chau, Member, IEEE, Behzad Moslehi, Senior Member, IEEE, and Mark R. Cutkosky, Member, IEEE. Exoskeletal Force Sensing End-Effectors with Embedded Optical Fiber Bragg Grating Sensors. [8]J. Deng， H. Xiao， W. Huo, et al., “Optical fiber sensor-based detection of partial discharges in power transformers,” Optics & Laser Technology, Vol.33, No.5, pp.305-311, 2001. [9] G.C. Hill, R. Melamud, F.E. Declercq, et al., “SU-8MEMS Fabry-Perot pressure sensor”, Sens. Actuators A: Phys., Vol.138, No.1, pp.52-62, 2007. [10] Edvard Cibula, Denis Donlagic, “Miniature fiber-optic pressure sensor with a polymer diaphragm”, Appl. Opt., Vol.44, No.14, pp.27362744, 2005. [10] Ge Yi-xian, Wang Ming, Chen Xu-xing, Li Ming, “A novel Fabry-Perot MEMS fiber pressure sensor based on intensity demodulation method interferometry”, Chinese Journal of Sensors and Actuators, vol.19, no.3, pp.1832-1839, 2006. [11] Xiaopei Chen, Fabin Shen, Anbo Wang, et.al., «Novel Fabry-Perot fiber optic sensor with multiple applications», Sensors for Harsh Environments, Bellingham, WA, Proc. of SPIE, Vol. 5590, pp.111-121, 2004. [12] Martellucci, S. Optical Sensors and Microsystems [Текст]/ S. Martellucci, A.N. Chester, A.G. Mignan -Boston: Kluwer academic publishers, 2002. -318 pp. [13] Matyunin S. Fiber-optical sensors based on mono-crystal films of garnet ferrites for mechatronic systems (2015) // Procedia Engineering. Vol. 106 . P. 202-209 [14] Matyunin S. Conntactkess FiberOptic Vibration Sensors for explosive Manufacturings (2015)// Book of abstracts "The 22 International Congress on Sound and Vibration, 12-16 July 2015, Florence (Italy)", The International Institute of Acoustics and Vibration (IIAV) and the Acoustical Society of Italy (AIA), P. 150-151. [15] Ana S. Silva, André Catarino, Miguel V. Correia, Orlando Frazão, «Design and characterization of a wearable macrobending fiber optic sensor for human joint angle determination», SPIE, Optical Engineering 52(12), No.126106, 2013. [16] Mitsuhiro Iga, Kyouko Hirama, Shusaku Hotta, et.al., «A novel fiber optic sensor using hetero-core structures and its applications», Optical Engineering for Sensing and Nanotechnology (ICOSN 2001), Proceedings of SPIE, Vol.4416, pp.78-81, 2001. [17] Luca Palmieri1, Luca Schenato. Distributed Optical Fiber Sensing Based on Rayleigh Scattering. The Open Optics Journal, 2013, 7, (Suppl1, M7) 104-127 [18] A.V. Hlybov, Volokonno-opticheskie polyarimetricheskie datchiki fizicheskih velichin [Fiber-optical polarimetric sensors of physical quantities]. The thesis on degree of the candidate of physical and mathematical sciences. St. Petersburg, 2004, P. 215. (in Russian)
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[19] I.V. Shilova, O.A. Belskaya, A.B. Sotsky, Ehlektrodinamicheskaya model izgibnogo volokonno opticheskogo datchika davleniya [Electrodynamic model of the flexural fiber optic pressure sensor]. Problems of physics, mathematics and technology, No. 1 (14), 2013, pp. 43-47. (in Russian)
ScienceDirect Procedia Engineering 176 (2017) 128 – 136
Dynamics and Vibroacoustics of Machines (DVM2016)
Research on characteristics of fiber optic sensors for anthropomorphous robots Sergey A. Matyunin* Samara National Research University, Moskovskoe shosse 34, Samara, 443086, Russian Federation
Abstract Structure, operating principle, theoretical provisions, experimental characteristics of fiber optic sensors for control of a bending in phalanxes of the anthropomorphous robot fingers, as well as principle of compensation for cross impact of adjacent measuring channels are considered. Linearization algorithm of positional characteristic of a sensor is given. The use of compensation algorithms of the cross impact and the linearization of the positional characteristic of sensing element offered to reduce nonlinearity of the sensor positional characteristic to 1% and to reduce the cross impact of different measuring channels to minus 20 dB, which is confirmed by experimental studies. Results of the experimental studies revealed that even without application of special temperature correction methods, the sensors used possess sufficiently high stability. Their phalanx temperature coefficient does not exceed 0,08%/°C. Assessment of high-speed performance of system, taking into account computing opportunities of the electronic transceiver is carried out. Technical characteristics of sensor prototypes and the electronic transceiver of fiber optical system are given. © Published by Elsevier Ltd. Ltd. This is an open access article under the CC BY-NC-ND license © 2017 2016The TheAuthors. Authors. Published by Elsevier (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of organizing committee of the Dynamics and Vibroacoustics of Machines (DVM2016). Peer-review under responsibility of the organizing committee of the international conference on Dynamics and Vibroacoustics of Machines Keywords: System of fiber optic sensors; angular movements measuring; phalanxes of anthropomorphous robot fingers; compensation of cross impact of different measuring channels; algorithm of positional characteristic linearization; electronic transceiver structure.
1. General characteristics and problems of sensor creation for anthropomorphous robots In modern robotic platforms of land, air, space basing, and in anthropomorphous robots, “electric” measuring transducers (sensors) are generally used with output electric signal in a digital and analog format [1-3]. Such sensors
* Corresponding author. Tel.: +7-927-717-10-68; E-mail address: [email protected]
1877-7058 © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of the international conference on Dynamics and Vibroacoustics of Machines
doi:10.1016/j.proeng.2017.02.280
Sergey A. Matyunin / Procedia Engineering 176 (2017) 128 – 136
possess high metrological characteristics, which allow integrating them by relatively simple means into general communication line with central processor. On the other hand, a particularity of “electric” sensors is their relatively large dimensions and a high sensitivity to external electromagnetic fields, as well, as creation of own electromagnetic field that is not always desirable. High sensitivity to the external electromagnetic fields and to ionizing radiation imposes restrictions and creates certain problems in their use, for example, in robots for repairing space international stations in conditions of near-earth space. This is particularly evident in development of manipulator sensors and smart skin of the anthropomorphous robots. At the same time, implementation of spatial position sensors in manipulators, captures and tactile sensors of the anthropomorphous robots based on principles of creation fiber-optic measuring systems [3, 7 -11] allows reducing overall dimensions of sensing elements by 3-5 times, placing electronic transceivers for sensors out in a remote case with special protection, in which the central processor of the robot can be placed connecting them to each other via optical fiber that is insensitive to an electromagnetic impulse and ionizing radiation. The overall dimensions of the sensing element of the sensor and the communication fiber line are mainly defined by optical fiber dimensions (0,30,9 mm in diameter). Of particular interest are fiber-optic sensors (FOS) with a closed optical channel, as fundamentally “nonelectrical” and non-subject to contamination of the optical channel. For autonomous robots, operator-controlled manipulators and exoskeletons, the most important problem is obtaining a reliable information about the state (position) of the executive power bodies and about force-torque perceptions transmitted to the operator. Such measuring systems can be implemented on the basis of fiber-optic position sensors (displacement) [6 - 12]. By the time, a set of FOS for movements based on conversion to amplitude and phase shift keying of radiation and to shift of a spectral characteristic in optical radiation, etc. [4-19] has been developed. Presently, a lot of displacement FOS was developed based on the transformation to amplitude and phase modulation of radiation, shifting the spectral characteristics of optical radiation, etc. [5-13, 17]. At the same time, despite all prospects of the FOS, their ubiquity is not observed. This is due to high cost of equipment (mainly the cost of electronic transceiver), lack of unification, and a small assortment of the FOS produced. Thus, the relevance of works on creation of new FOS is determined by their major advantages over the “electric” sensors and the incompleteness of research in the field of creation of specialized FOS with different physical values for specific tasks of controlling robotic mobile platforms. Purpose of researches is development and research of FOS system for angular movements measuring of phalanxes of the anthropomorphous robot fingers. 2. Principle of operation Discussed FOS measuring systems (MS) of phalanxes angular movements of the anthropomorphous robot fingers are based on modulation of bending losses in optical fiber during its deformation. The MS (Fig. 1) consists of electronic transceiver (ET) placed remotely from the FOS, fiber optic sensors (FOS1-FOS3) and fiber-optic communication lines (FOCL) connecting the FOS1-FOS3 with the ET. The structure of the ET includes: power module (PM), reference-voltage source (RVS), laser diode (LD) connected to a power source (LDPS) with a circuit of optical radiation stabilization, optical splitter (OS) with a number of output channels according to the number of robot fingers phalanxes distributing optical radiation on the FOS1-FOS3, inverse optical splitters (IOS1- IOS3), for example, made in the form of circulators separating FOS1FOS3 signals from LD signal. The FOS-FOS3 are located in the joints of the robot fingers phalanxes. FOS1-FOS3 optical signals via the corresponding IOS1-IOS3 are transmitted to photodetectors (PD1-PD3), which is then digitized and converted in the analog-to-digital converter (ADC) and microprocessor computing device (MCD). The MCD is connected to the onboard control system (OCS). Wiring scheme of a sensitive optical fiber in one of fingers of the robot is given in Fig. 2. Properly, sensitive elements of the FOS1-FOS3 represent segments of optical fiber with multi-layer metallized coating in a polymer shell with 0.3-0.9 mm diameter. When the phalanxes of the robot finger bend, corresponding segments of the
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sensitive optical fiber is deformed (bending) and, as a result, a part of the optical radiation is output to the optical fiber cladding and is absorbed by it, thus changing the optical transmittance of radiation. The FOS sensitivity calculation is reduced to the calculation of the radiation losses due to bending of the optical fiber. However, in this case, it is necessary to distinguish “useful information” regarding optical radiation modulation and “interfering information” regarding modulation. For example, FOS1 signal (Fig. 2) is not influenced by the deformation of the optical fiber of phalanxes 2–3 (but the FOS1 signal is influenced by the deformation of the optical fiber in its hand-to-phalanxes articulation 1, not shown in Fig. 2). FOS2 signal is influenced by the deformation of its optical fiber in the phalanx-to-hand articulation 1. FOS3 signal is influenced by the deformation of its optical fiber in the phalanx 1-to-phalanx 2 articulation. The bending of the optical fiber in the hand influences all of the FOS1-FOS3 signals.
Fig 1. Structure scheme of the SM.
Fig. 2. The wiring diagram of sensitive optical fiber.
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Deformation of sensitive optical fiber is characterized by radii of local fiber bendings within its laying inside the robot’s hand. As light travels along the fiber in the form of modes, attenuation of each of these modes depends essentially on the fiber bending radius [15-17]. In the sensor considered, the bending shape of the optical fiber in the FOS1-FOS3 is determined by the method of its mounting on the phalanxes of the robot (Fig. 3). Option 1. Motionless fixing of the optical fiber on axis (pulley) of a finger phalanx (point b, Fig. 3) with movable fixing in points a, c of phalanxes of fingers. Option 2. Motionless fixing of the optical fiber in points a, c of finger phalanx with movable fixing in point b. The first option of fixing practically results in that finger phalanx rotation causes the optic fiber to slip at the fixing points a, c due to elongation/shortening of the fiber. In addition, when the phalanxes turn on the angle φ, a double “fiber fracture” is observed at the point b. It is obvious, that in order to avoid optical fiber breakage, its excess/shortage on the right and on left of the b point has to be compensated by an additional loop of the optical fiber in the phalanxes of the fingers. The second option of fixing is more preferable, as there is no movement of the optical fiber in phalanxes of fingers, the excess/shortage of the optical fiber is compensated by radius RP alteration of the optical fiber loop.
Fig. 3. Scheme of fixing sensitive optical fiber.
In the Figure 3 the following references are accepted: Ro – pulley diameter, which forms a curve of the optical fiber bending; [0, max ] - current and maximum rotation angles of the finger phalanxes; RL , RL0 - initial (at ϕ=0) and current radius of the optical fiber loop. The current radius of the optical fiber loop is defined by expression: RL RL0 R0
. 2
(1)
The form of a bending shape of the optical fiber passing by the FOS1-FOS3 is close to circular and can be set by one radius of RP determined by points of fastening the optical fiber to the phalanxes of the fingers (Fig. 4): RP
d , sin ( / 2)
(2)
where d – distance from the optical fiber fastening point in the finger phalanxes to the axis of its rotation. Neglecting mutual transformation of modes in articulation places of radial and straight segments of the optical fiber, using ratios of modes orthogonality and assuming that modes of fiber cladding are effectively filtered by the absorbing polymeric covering, the power losses of optical radiation (curve 1, Fig. 5) are determined by the method described in [18,19]. According to [17-19] a good coincidence of theoretical and experimental results is observed. However, as results of more thorough research show, the real results are significantly different. It can be explained by a small number of
132
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experimental points in [17-19] for comparing theoretical and practical results (the experimental points just “missed” sections with sharp change character of power losses curve), and by neglecting the polarizing beats occurring due to polarization of radiation in fiber at its bending and interference.
Fig. 4. The bending shape of the optical fiber passing FOS1-FOS3
In Figure 5, curve 2 (a selection of 20 points is given) represents character of power losses curve (experimental values). It may be well observed that in section ϕ1-ϕ2 not only the sharp deviation of an experimental curve from theoretical one is observed, but also, there is an ambiguity in measurement of signal losses value of the FOS. At the same time, by selecting for operation the sections of the curve, where the ambiguity of sensor measurements is not observed, it is possible to approximate with an adequate accuracy the dependence of the FOS signal losses on the linear relation (Fig. 6).
Fig. 5. The dependence of optical losses at bending of sensitive optical fiber: 1 – theoretical losses not accounting polarizing beats; 2 – experimental results of losses.
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Fig. 6. The dependence of optical losses at bending of sensitive optical fiber in relative units with linear approximation.
Considering the observations above, the expressions for signals Y1, Y2, Y3 of corresponding detectors FOS1, FOS2, FOS3 shall have the following form. For FOS1 installation segment of the bending losses curve (partial fiber losses): Y11 (1 ) [e11 f11 ( RLO RO
1 )], 2 ],
d Sin(1 / 2) d 1 1 1 Y3 (1 ) [e3 f 3 ], Sin(1 / 2) Y21 (1 ) [e21 f 21
(3)
where: eij , f i j - coefficients of linear approximation for optical fiber segment of i-phalanx and j-detector; i rotation angle of i-phalanx. For FOS2 installation segment (partial fiber losses): Y21 (2 ) [e22 f 22 ( RLO RO Y32 (2 ) [e32 f32
d Sin(2 / 2)
2 )], 2 ].
(4)
For FOS3 installation segment (partial fiber losses): Y33 (3 ) [e33 f 33 ( RLO RO
3 )]. 2
Thus, complete signals of the FOS1-FOS3 shall be as follows:
(5)
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1 )], 2 d Y2 (1 , 2 ) Y21 Y22 [e12 f 21 ] [e22 f 22 ( RLO RO 2 )], Sin(1 / 2) 2 d d Y3 (1 , 2 , 3 ) Y31 Y32 Y33 [e31 f 31 ] [e32 f 32 ] [e33 f33 ( RLO RO 3 )]. 2 Sin(1 / 2) Sin(2 / 2) Y1 (1 ) [e11 f11 ( RLO RO
(6)
Expressing ϕ1, ϕ2, ϕ3 angle values in an explicit form resulting from the corresponding Y1(ϕ1), Y2(ϕ1, ϕ2), Y3(ϕ1, ϕ2, ϕ3) dependences, it is possible to obtain Y1(ϕ1), Y2(ϕ2), Y3(ϕ3) dependences in an explicit form. 3. Experimental studies and technical specifications Experimental studies of transient response of FOS1, FOS2, FOS3 fixed on the model of a three-phalanx hand of anthropomorphous AP600 robot (Fig. 7) were conducted. The main results of experimental studies are given in Fig. 5-6 and in Table 1.
Fig. 7. The FOS fixed on the hand of the anthropomorphous AP600 robot, the communication line and the ET. Table 1. Technical specification of FOS and ET. Object
Basic characteristics
FOS
1.Diameter, mm
0,9
2.Length of the connecting optical fiber cable up to, m
10
3.Measured rotation angle of phalanx of finger, degrees
from 0 to 60
4.Resolution capability, binary digit bit 5.Nonlinearity of the position characteristic, % 6.Reduced temperature coefficient, %/°C ET
Value
1.Number of measuring channels 2.Dimensions, mm
10 1 0,08 8 135х85х40
3.Power supply voltage, V
5
4.Current consumption, A
0,35
5.Output signal
SPI
6.Cross impact of measuring channels up to, dB 7.Sampling frequency of FOS, ms 8.Operating temperature, °C
minus 20 10 from 0 to +50
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4. Conclusion The following results of theoretical and experimental studies were obtained: Dependence between the “beats” value of the FOS positional characteristic and the value of its deformation was revealed. The polarizing beats value is up to 5-7 dB; The compensation principle of cross impact for adjacent measuring channels was developed. The cross impact of measuring channels is reduced to minus 20 dB. The nonlinearity of the position characteristic does not exceed 1%, and the reduced temperature coefficient of the FOS does not exceed 0,08%/°C; The experimental studies of the FOS characteristics confirm the theoretical researches. Acknowledgements The work was carried out with financial support of the Ministry of Education and Science of the Russian Federation. Unique ID: Applied research and experimental work RFMEF157816X0209. References [1] Kirsanov K. The Architecture of Robotics Control Software for Heterogeneous Mobile Robots Network (2014)// 24th DAAAM International Symposium on Intelligent Manufacturing and Automation, DAAM 2013. Procedia Engineering. Vol. 69, P. 216-221. [2] Laird, J. E., Wray, R. E. III, Marinier, R. P. III, & Langley, P. (2009). Claims and Challenges in Evaluating Human-Level Intelligent Systems // Proceedings of the Second Conference on Artificial General Intelligence. [3] Xiaoyi Bao * and Liang Chen. Recent Progress in Distributed Fiber Optic Sensors. Sensors 2012, 12, 8601-8639; doi:10.3390/s120708601. ISSN 1424-8220. www.mdpi.com/journal/sensors. [4] Gerkey B., Vaughan R., and Howard A. The Player/Stage Project: Tools for Multi-Robot and Distributed Sensor Systems (2003)// Proceedings of the International Conference on Advanced Robotics. P. 317-323. [5] Shizhuo, Yin. Fiber Optic Sensors (2008) // Yin Shizhuo, Paul B. Ruffin, T.S.Yu. Francis. –Boca Raton, London, New York : CRC Press, Taylor & Francis Group, P. 477. [6] Nielsen, M.D. Predicting macrobending loss for large-mode area photonic crystal fibers / M.D. Nielsen, N.A. Mortensen, M. Albertsen (2004) // Optics Express. Vol.7, P. 1775–1779. [7]Yong-Lae Park, Student Member, IEEE, Seok Chang Ryu, Richard J. Black, Member, IEEE, Kelvin K. Chau, Member, IEEE, Behzad Moslehi, Senior Member, IEEE, and Mark R. Cutkosky, Member, IEEE. Exoskeletal Force Sensing End-Effectors with Embedded Optical Fiber Bragg Grating Sensors. [8]J. Deng， H. Xiao， W. Huo, et al., “Optical fiber sensor-based detection of partial discharges in power transformers,” Optics & Laser Technology, Vol.33, No.5, pp.305-311, 2001. [9] G.C. Hill, R. Melamud, F.E. Declercq, et al., “SU-8MEMS Fabry-Perot pressure sensor”, Sens. Actuators A: Phys., Vol.138, No.1, pp.52-62, 2007. [10] Edvard Cibula, Denis Donlagic, “Miniature fiber-optic pressure sensor with a polymer diaphragm”, Appl. Opt., Vol.44, No.14, pp.27362744, 2005. [10] Ge Yi-xian, Wang Ming, Chen Xu-xing, Li Ming, “A novel Fabry-Perot MEMS fiber pressure sensor based on intensity demodulation method interferometry”, Chinese Journal of Sensors and Actuators, vol.19, no.3, pp.1832-1839, 2006. [11] Xiaopei Chen, Fabin Shen, Anbo Wang, et.al., «Novel Fabry-Perot fiber optic sensor with multiple applications», Sensors for Harsh Environments, Bellingham, WA, Proc. of SPIE, Vol. 5590, pp.111-121, 2004. [12] Martellucci, S. Optical Sensors and Microsystems [Текст]/ S. Martellucci, A.N. Chester, A.G. Mignan -Boston: Kluwer academic publishers, 2002. -318 pp. [13] Matyunin S. Fiber-optical sensors based on mono-crystal films of garnet ferrites for mechatronic systems (2015) // Procedia Engineering. Vol. 106 . P. 202-209 [14] Matyunin S. Conntactkess FiberOptic Vibration Sensors for explosive Manufacturings (2015)// Book of abstracts "The 22 International Congress on Sound and Vibration, 12-16 July 2015, Florence (Italy)", The International Institute of Acoustics and Vibration (IIAV) and the Acoustical Society of Italy (AIA), P. 150-151. [15] Ana S. Silva, André Catarino, Miguel V. Correia, Orlando Frazão, «Design and characterization of a wearable macrobending fiber optic sensor for human joint angle determination», SPIE, Optical Engineering 52(12), No.126106, 2013. [16] Mitsuhiro Iga, Kyouko Hirama, Shusaku Hotta, et.al., «A novel fiber optic sensor using hetero-core structures and its applications», Optical Engineering for Sensing and Nanotechnology (ICOSN 2001), Proceedings of SPIE, Vol.4416, pp.78-81, 2001. [17] Luca Palmieri1, Luca Schenato. Distributed Optical Fiber Sensing Based on Rayleigh Scattering. The Open Optics Journal, 2013, 7, (Suppl1, M7) 104-127 [18] A.V. Hlybov, Volokonno-opticheskie polyarimetricheskie datchiki fizicheskih velichin [Fiber-optical polarimetric sensors of physical quantities]. The thesis on degree of the candidate of physical and mathematical sciences. St. Petersburg, 2004, P. 215. (in Russian)
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