Electrode for Force Sensor of Conductive Rubber
Affiliation(s)
Department of Electrical and Computer Engineering, Akashi College of Technology, Hyogo, Japan. Department of Applied Analysis and Complex Dynamical Systems, Kyoto University, Kyoto, Japan.
Department of Electrical and Computer Engineering, Akashi College of Technology, Hyogo, Japan. Department of Applied Analysis and Complex Dynamical Systems, Kyoto University, Kyoto, Japan.
ABSTRACT
Tactile sensors are believed to be a key element in order to realize robotic fingers to catch a fragile object without damage. Force sensitive conductive rubber is a low-cost material and then attractive for the application to tactile sensors. We have studied the effect of electrodes attached to the rubber sheets. We have tried four kinds of electrodes: vacuum deposited Al, adhesive Cu tape, Al thin film sheet and silver paste. It can be concluded that vacuum deposited Al has the highest potential from the practical point of view; it has the widest dynamic range and good precision at the same time.
Tactile sensors are believed to be a key element in order to realize robotic fingers to catch a fragile object without damage. Force sensitive conductive rubber is a low-cost material and then attractive for the application to tactile sensors. We have studied the effect of electrodes attached to the rubber sheets. We have tried four kinds of electrodes: vacuum deposited Al, adhesive Cu tape, Al thin film sheet and silver paste. It can be concluded that vacuum deposited Al has the highest potential from the practical point of view; it has the widest dynamic range and good precision at the same time.
Cite this paper
M. Ohmukai, Y. Kami and R. Matsuura, "Electrode for Force Sensor of Conductive Rubber," Journal of Sensor Technology, Vol. 2 No. 3, 2012, pp. 127-131. doi: 10.4236/jst.2012.23018.
M. Ohmukai, Y. Kami and R. Matsuura, "Electrode for Force Sensor of Conductive Rubber," Journal of Sensor Technology, Vol. 2 No. 3, 2012, pp. 127-131. doi: 10.4236/jst.2012.23018.
References
[1] M. H. Lee and H. R. Nicholls, “Review Article Tactile Sensing for Mechatronics—A State of the Art Survey,” Mechatronics, Vol. 9, No. 1, 1999, pp. 1-31. doi:10.1016/S0957-4158(98)00045-2 [2] Z. Li, P. Hsu and S. Sastry, “Grasping and Coordinated Manipulation by a Multifingered Robot Hand,” International Journal of Robotics Research, Vol. 8, No. 4, 1989, pp. 33-50. doi:10.1177/027836498900800402 [3] A. D. Berger and P. K. Khosla, “Using Tactile Data for Real-Time Feedback,” International Journal of Robotics Research, Vol. 10, No. 2, 1991, pp. 88-102. doi:10.1177/027836499101000202 [4] P. A. Schmidt, E. Mael and R. P. Wurtz, “A Sensor for Dynamic Tactile Information with Applications in Human-Robot Interaction & Object Exploration,” Robotics and Autonomous Systems, Vol. 54, No. 12, 2006, pp. 1005-1014. doi:10.1016/j.robot.2006.05.013 [5] K. Kim, K. R. Lee, W. H. Kim, K. Park, T. Kim, J. Kim and J. J. Pak, “Polymer-Based Flexible Tactile Sensor Up to 32 × 32 Arrays Integrated with Interconnection Teminals,” Sensors and Actuators A: Physical, Vol. 156, No. 2, 2009, pp. 284-291. doi:10.1016/j.sna.2009.08.015 [6] J. Engel, J. Chen and C. Liu, “Development of Polyimide Flexible Tactile Sensor Skin,” Journal of Micromechanics and Microengineering, Vol. 13, No. 3, 2003, pp. 359-366. doi:10.1088/0960-1317/13/3/302 [7] Y. Zhang, “Sensitivity Enhancement of a Micro-Scale Biomimetic Tactile Sensor with Epidermal Ridges,” Journal of Micromechanics and Microengineering, Vol. 20, No. 8, 2010, Article ID: 085012. doi:10.1088/0960-1317/20/8/085012 [8] W.-C. Choi, “Polymer Micromachined Flexible Tactile Sensor for Three-Axial Toads Detection,” Transactions on Electrical and Electronic Materials, Vol. 11, No. 3, 2010, pp. 130-133. doi:10.4313/TEEM.2010.11.3.130 [9] K. Noda, K. Hoshino, K. Matsumoto and I. Shimoyama, “A Shear Stress Sensor for Tactile Sensing with the Piezoresistive Cantilever Standing in Elastic Material,” Sensors and Actuators A: Physical, Vol. 127, No. 2, 2006, pp. 295-301. doi:10.1016/j.sna.2005.09.023 [10] L. Beccai, S. Rocdella, L. Ascari, P. Valdastri, A. Sieber, M. Carrozza and P. Dario, “Development and Experimental Analysis of a Soft Compliant Tactile Microsensor for Anthropomorphic Artificial Hand,” IEEE/ASME Transactions on Mechatronics, Vol. 13, No. 2, 2008, pp. 158-168. doi:10.1109/TMECH.2008.918483 [11] H. Lee, J. Chung, S. Chang and E. Yoon, “Normal and Shear Force Measurement Using a Flexible Polymer Tactile Sensor with Embedded Multiple Capacitors,” Journal of Microelectromechanical Systems, Vol. 17, No. 4, 2008, pp. 934-942. doi:10.1109/JMEMS.2008.921727 [12] S. Miyazaki and A. Ishida, “Capacitive Transducer for Continuous Measurement of Vertical Foot Force,” Medical and Biological Engineering and Computing, Vol. 22, No. 4, 1984, pp. 309-316. doi:10.1007/BF02442098 [13] Y. Hasegawa, M. Shikida, D. Ogura, Y. Suzuki and K. Sato, “Fabrication of a Wearable Fabric Tactile Sensor Produced by Artificial Hollow Fiber,” Journal of Micromechanics and Microengineering, Vol. 18, No. 8, 2008, Article ID: 085014. doi:10.1088/0960-1317/18/8/085014 [14] J.-S. Heo, J.-H. Chung and J.-J. Lee, “Tactile Sensor Arrays Using Fiber Bragg Grating,” Sensors and Actuators A: Physical, Vol. 126, No. 2, 2006, pp. 312-327. doi:10.1016/j.sna.2005.10.048 [15] E. Cheung and V. L. Lumelsky, “A Sensitive Skin System for Motion Control of Robot Arm Manipulators,” Robotics and Autonomous Systems, Vol. 10, No. 1, 1992, pp. 9-32. doi:10.1016/0921-8890(92)90012-N [16] E. S. Kolesar, R. R. Reston, D. G. Ford and R. C. Fitch, “Multiplexed Piezoelectric Polymer Tactile Sensor,” Journal of Robotic Systems, Vol. 9, No. 1, 1992, pp. 37-63. doi:10.1002/rob.4620090104 [17] J. Dargahi, M. Parameswaran and S. Payandeh, “A Micromachined Piezoelectric Tactile Sensor for an Endoscopic Grasper—Theory, Fabrication and Experiments,” Journal of Microelectromechanical Systems, Vol. 9, No. 3, 2000, pp. 329-335. doi:10.1109/84.870059 [18] J. R. Flanagan and A. M. Wing, “Modulation of Grip Force with Load Force during Point-To-Point Arm Movements,” Experimental Brain Research, Vol. 95, No. 1, 1993, pp. 131-143. doi:10.1007/BF00229662 [19] P. Dario and D. de Rossi, “Tactile Sensors and Gripping Challenge,” IEEE Spectrum, Vol. 22, 1985, pp. 46-52. [20] N. Wettels, V. Santos, R. Johansson and G. Loeb, “Biomimetric Tactile Sensor Array,” Advanced Robotics, Vol. 22, No. 8, 2008, pp. 829-849. doi:10.1163/156855308X314533 [21] I. Manunza and A. Bonfiglio, “Pressure Sensing Using a Completely Flexible Organic Transistor,” Biosensors and Bioelectronics, Vol. 22, No. 12, 2007, pp. 2775-2779. doi:10.1016/j.bios.2007.01.021 [22] T. Sekitani and T. Someya, “Stretchable, Large-Area Organic Electronics,” Advanced Materials, Vol. 22, No. 2, 2010, pp. 2228-2246. doi:10.1002/adma.200904054 [23] D. Bloor, K. Donnelly, P. J. Hands, P. Laughlin and D. Lussey, “A Metal-Polymer Composite with Unusal Properties,” Journal of Physics D: Applied Physics, Vol. 38, No. 16, 2005, pp. 2851-2860. doi:10.1088/0022-3727/38/16/018 [24] V. Maheshwari and R. F. Saraf, “High-Resolution Thin-Film Device to Sense Texture by Touch,” Science, Vol. 312, No. 5779, 2006, pp. 1501-1504. doi:10.1126/science.1126216 [25] S. Ando and H. Shinoda, “Ultrasonic Emission Tactile Sensing,” IEEE on Control System, Vol. 15, No. 1, 1995, pp. 61-69. doi:10.1109/37.341866 [26] R. S. Dahiya, M. Valle and L. Lorenzelli, “Spice Model of Lossy Piezoelectric Polymers,” IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, Vol. 56, No. 2, 2009, pp. 387-396. doi:10.1109/TUFFC.2009.1048 [27] G. M. Krishna and K. Rajanna, “Tactile Sensor Based on Piezoelectric Resonance,” IEEE Sensors Journal, Vol. 4, No. 5, 2004, pp. 691-697. doi:10.1109/JSEN.2004.833505 [28] T. J. Nelson, R. B. V. Dover, S. Jin, S. Hackwood and G. Beni, “Shear-Sensitive Magnetroresistive Robotic Tactile Sensor,” IEEE Transactions on Magnetics, Vol. 22, No. 5, 1986, pp. 394-396. doi:10.1109/TMAG.1986.1064386 [29] Z. Wen, Y. Wu, Z. Zhang, S. Xu, S. Huang and Y. Li, “Development of an Integrated Vacuum Microelectronic Tactile Sensor Array,” Sensors and Actuators A: Physical, Vol. 103, No. 3, 2003, pp. 301-306. doi:10.1016/S0924-4247(02)00392-8 [30] D. J. Beebe, A. S. Hsieh, D. D. Denton and R. G. Radwin, “A Silicon Force Sensor for Robotics and Medicine,” Sensors and Actuators A: Physical, Vol. 50, No. 1-2, 1995, pp. 55-65. doi:10.1016/0924-4247(96)80085-9 [31] M. R. Wolffenbuttel and P. P. L. Regtien, “Polysilicon Bridges for the Realization of Tactile Sensors,” Sensors and Actuators A: Physical, Vol. 26, No. 1-3, 1991, pp. 257-264. doi:10.1016/0924-4247(91)87002-K [32] S. Sugiyama, K. Kawahata, M. Yoneda and I. Igarashi, “Tactile Image Detection Using a 1k-Element Silicon Pressure Sensor Array,” Sensors and Actuators A: Physical, Vol. 22, No. 1-3, 1990, pp. 397-400. [33] L. Liu, X. Zheng and L. Zhijian, “An Array Tactile Sensor with Piezoresistive Single-Crystal Silicon Diaphragm,” Sensors and Actuators A: Physical, Vol. 35, No. 3, 1993, pp. 193-196. doi:10.1016/0924-4247(93)80151-6 [34] B. J. Kane, M. R. Cutkosky and G. T. A. Kovacs, “A Traction Stress Sensor Array for Use in High-Resolution Robotic Tactile Imaging,” Journal of Microelectromechanical Systems, Vol. 9, No. 4, 2000, pp. 425-434. doi:10.1109/84.896763 [35] H. Takao, K. Sawada and M. Ishida, “Monolithic Silicon Smart Tactile Image Sensor with Integrated Strain Sensor Array on Pneumatically Swollen Single-Diaphragm Structure,” IEEE Transactions on Electron Devices, Vol. 53, No. 5, 2006, pp. 1250-1259. doi:10.1109/TED.2006.872698 [36] Z. Chu, P. M. Saoor and S. Middelhoek, “Silicon Three-Axial Tactile Sensor,” Sensors and Actuators A: Physical, Vol. 54, No. 1-3, 1996, pp. 505-510. doi:10.1016/S0924-4247(95)01190-0 [37] M. Leineweber, G. Pelz, M. Schmidt, H. Kappert and G. Zimmer, “New Tactile Sensor Chip with Silicone Rubber Cover,” Sensors and Actuators A: Physical, Vol. 84, No. 3, 2000, pp. 236-245. doi:10.1016/S0924-4247(00)00310-1 [38] Y.-J. Yang, M.-Y. Cheng, W.-Y. Chang, L.-C. Tsao, S.-A. Yang, W.-P. Shih, F.-Y. Chang, S.-H. Chang and K.-C. Fang, “An Integrated Flexible Temperature and Tactile Sensing Array Using PI-Copper Films,” Sensors and Actuators A: Physical, Vol. 143, No. 1, 2008, pp. 143-153. doi:10.1016/j.sna.2007.10.077 [39] R. H. LaMotte and M. A. Srinivasan, “Tactile Discrimination of Shape: Responses of Slowly Adapting Mechanoreceptive Afferents to a Step Stroked across the Monkey Fingerpad,” Journal of Neuroscience, Vol. 7, No. 6, 1987, pp. 1655-1671. [40] R. H. LaMotte and M. A. Srinivasan, “Tactile Discrimination of Shape: Responses of Rapidly Adapting Mechanoreceptive Afferents to a Step Stroked across the Monkey Fingerpad,” Journal of Neuroscience, Vol. 7, No. 6, 1987, pp. 1672-1681.
[1] M. H. Lee and H. R. Nicholls, “Review Article Tactile Sensing for Mechatronics—A State of the Art Survey,” Mechatronics, Vol. 9, No. 1, 1999, pp. 1-31. doi:10.1016/S0957-4158(98)00045-2 [2] Z. Li, P. Hsu and S. Sastry, “Grasping and Coordinated Manipulation by a Multifingered Robot Hand,” International Journal of Robotics Research, Vol. 8, No. 4, 1989, pp. 33-50. doi:10.1177/027836498900800402 [3] A. D. Berger and P. K. Khosla, “Using Tactile Data for Real-Time Feedback,” International Journal of Robotics Research, Vol. 10, No. 2, 1991, pp. 88-102. doi:10.1177/027836499101000202 [4] P. A. Schmidt, E. Mael and R. P. Wurtz, “A Sensor for Dynamic Tactile Information with Applications in Human-Robot Interaction & Object Exploration,” Robotics and Autonomous Systems, Vol. 54, No. 12, 2006, pp. 1005-1014. doi:10.1016/j.robot.2006.05.013 [5] K. Kim, K. R. Lee, W. H. Kim, K. Park, T. Kim, J. Kim and J. J. Pak, “Polymer-Based Flexible Tactile Sensor Up to 32 × 32 Arrays Integrated with Interconnection Teminals,” Sensors and Actuators A: Physical, Vol. 156, No. 2, 2009, pp. 284-291. doi:10.1016/j.sna.2009.08.015 [6] J. Engel, J. Chen and C. Liu, “Development of Polyimide Flexible Tactile Sensor Skin,” Journal of Micromechanics and Microengineering, Vol. 13, No. 3, 2003, pp. 359-366. doi:10.1088/0960-1317/13/3/302 [7] Y. Zhang, “Sensitivity Enhancement of a Micro-Scale Biomimetic Tactile Sensor with Epidermal Ridges,” Journal of Micromechanics and Microengineering, Vol. 20, No. 8, 2010, Article ID: 085012. doi:10.1088/0960-1317/20/8/085012 [8] W.-C. Choi, “Polymer Micromachined Flexible Tactile Sensor for Three-Axial Toads Detection,” Transactions on Electrical and Electronic Materials, Vol. 11, No. 3, 2010, pp. 130-133. doi:10.4313/TEEM.2010.11.3.130 [9] K. Noda, K. Hoshino, K. Matsumoto and I. Shimoyama, “A Shear Stress Sensor for Tactile Sensing with the Piezoresistive Cantilever Standing in Elastic Material,” Sensors and Actuators A: Physical, Vol. 127, No. 2, 2006, pp. 295-301. doi:10.1016/j.sna.2005.09.023 [10] L. Beccai, S. Rocdella, L. Ascari, P. Valdastri, A. Sieber, M. Carrozza and P. Dario, “Development and Experimental Analysis of a Soft Compliant Tactile Microsensor for Anthropomorphic Artificial Hand,” IEEE/ASME Transactions on Mechatronics, Vol. 13, No. 2, 2008, pp. 158-168. doi:10.1109/TMECH.2008.918483 [11] H. Lee, J. Chung, S. Chang and E. Yoon, “Normal and Shear Force Measurement Using a Flexible Polymer Tactile Sensor with Embedded Multiple Capacitors,” Journal of Microelectromechanical Systems, Vol. 17, No. 4, 2008, pp. 934-942. doi:10.1109/JMEMS.2008.921727 [12] S. Miyazaki and A. Ishida, “Capacitive Transducer for Continuous Measurement of Vertical Foot Force,” Medical and Biological Engineering and Computing, Vol. 22, No. 4, 1984, pp. 309-316. doi:10.1007/BF02442098 [13] Y. Hasegawa, M. Shikida, D. Ogura, Y. Suzuki and K. Sato, “Fabrication of a Wearable Fabric Tactile Sensor Produced by Artificial Hollow Fiber,” Journal of Micromechanics and Microengineering, Vol. 18, No. 8, 2008, Article ID: 085014. doi:10.1088/0960-1317/18/8/085014 [14] J.-S. Heo, J.-H. Chung and J.-J. Lee, “Tactile Sensor Arrays Using Fiber Bragg Grating,” Sensors and Actuators A: Physical, Vol. 126, No. 2, 2006, pp. 312-327. doi:10.1016/j.sna.2005.10.048 [15] E. Cheung and V. L. Lumelsky, “A Sensitive Skin System for Motion Control of Robot Arm Manipulators,” Robotics and Autonomous Systems, Vol. 10, No. 1, 1992, pp. 9-32. doi:10.1016/0921-8890(92)90012-N [16] E. S. Kolesar, R. R. Reston, D. G. Ford and R. C. Fitch, “Multiplexed Piezoelectric Polymer Tactile Sensor,” Journal of Robotic Systems, Vol. 9, No. 1, 1992, pp. 37-63. doi:10.1002/rob.4620090104 [17] J. Dargahi, M. Parameswaran and S. Payandeh, “A Micromachined Piezoelectric Tactile Sensor for an Endoscopic Grasper—Theory, Fabrication and Experiments,” Journal of Microelectromechanical Systems, Vol. 9, No. 3, 2000, pp. 329-335. doi:10.1109/84.870059 [18] J. R. Flanagan and A. M. Wing, “Modulation of Grip Force with Load Force during Point-To-Point Arm Movements,” Experimental Brain Research, Vol. 95, No. 1, 1993, pp. 131-143. doi:10.1007/BF00229662 [19] P. Dario and D. de Rossi, “Tactile Sensors and Gripping Challenge,” IEEE Spectrum, Vol. 22, 1985, pp. 46-52. [20] N. Wettels, V. Santos, R. Johansson and G. Loeb, “Biomimetric Tactile Sensor Array,” Advanced Robotics, Vol. 22, No. 8, 2008, pp. 829-849. doi:10.1163/156855308X314533 [21] I. Manunza and A. Bonfiglio, “Pressure Sensing Using a Completely Flexible Organic Transistor,” Biosensors and Bioelectronics, Vol. 22, No. 12, 2007, pp. 2775-2779. doi:10.1016/j.bios.2007.01.021 [22] T. Sekitani and T. Someya, “Stretchable, Large-Area Organic Electronics,” Advanced Materials, Vol. 22, No. 2, 2010, pp. 2228-2246. doi:10.1002/adma.200904054 [23] D. Bloor, K. Donnelly, P. J. Hands, P. Laughlin and D. Lussey, “A Metal-Polymer Composite with Unusal Properties,” Journal of Physics D: Applied Physics, Vol. 38, No. 16, 2005, pp. 2851-2860. doi:10.1088/0022-3727/38/16/018 [24] V. Maheshwari and R. F. Saraf, “High-Resolution Thin-Film Device to Sense Texture by Touch,” Science, Vol. 312, No. 5779, 2006, pp. 1501-1504. doi:10.1126/science.1126216 [25] S. Ando and H. Shinoda, “Ultrasonic Emission Tactile Sensing,” IEEE on Control System, Vol. 15, No. 1, 1995, pp. 61-69. doi:10.1109/37.341866 [26] R. S. Dahiya, M. Valle and L. Lorenzelli, “Spice Model of Lossy Piezoelectric Polymers,” IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, Vol. 56, No. 2, 2009, pp. 387-396. doi:10.1109/TUFFC.2009.1048 [27] G. M. Krishna and K. Rajanna, “Tactile Sensor Based on Piezoelectric Resonance,” IEEE Sensors Journal, Vol. 4, No. 5, 2004, pp. 691-697. doi:10.1109/JSEN.2004.833505 [28] T. J. Nelson, R. B. V. Dover, S. Jin, S. Hackwood and G. Beni, “Shear-Sensitive Magnetroresistive Robotic Tactile Sensor,” IEEE Transactions on Magnetics, Vol. 22, No. 5, 1986, pp. 394-396. doi:10.1109/TMAG.1986.1064386 [29] Z. Wen, Y. Wu, Z. Zhang, S. Xu, S. Huang and Y. Li, “Development of an Integrated Vacuum Microelectronic Tactile Sensor Array,” Sensors and Actuators A: Physical, Vol. 103, No. 3, 2003, pp. 301-306. doi:10.1016/S0924-4247(02)00392-8 [30] D. J. Beebe, A. S. Hsieh, D. D. Denton and R. G. Radwin, “A Silicon Force Sensor for Robotics and Medicine,” Sensors and Actuators A: Physical, Vol. 50, No. 1-2, 1995, pp. 55-65. doi:10.1016/0924-4247(96)80085-9 [31] M. R. Wolffenbuttel and P. P. L. Regtien, “Polysilicon Bridges for the Realization of Tactile Sensors,” Sensors and Actuators A: Physical, Vol. 26, No. 1-3, 1991, pp. 257-264. doi:10.1016/0924-4247(91)87002-K [32] S. Sugiyama, K. Kawahata, M. Yoneda and I. Igarashi, “Tactile Image Detection Using a 1k-Element Silicon Pressure Sensor Array,” Sensors and Actuators A: Physical, Vol. 22, No. 1-3, 1990, pp. 397-400. [33] L. Liu, X. Zheng and L. Zhijian, “An Array Tactile Sensor with Piezoresistive Single-Crystal Silicon Diaphragm,” Sensors and Actuators A: Physical, Vol. 35, No. 3, 1993, pp. 193-196. doi:10.1016/0924-4247(93)80151-6 [34] B. J. Kane, M. R. Cutkosky and G. T. A. Kovacs, “A Traction Stress Sensor Array for Use in High-Resolution Robotic Tactile Imaging,” Journal of Microelectromechanical Systems, Vol. 9, No. 4, 2000, pp. 425-434. doi:10.1109/84.896763 [35] H. Takao, K. Sawada and M. Ishida, “Monolithic Silicon Smart Tactile Image Sensor with Integrated Strain Sensor Array on Pneumatically Swollen Single-Diaphragm Structure,” IEEE Transactions on Electron Devices, Vol. 53, No. 5, 2006, pp. 1250-1259. doi:10.1109/TED.2006.872698 [36] Z. Chu, P. M. Saoor and S. Middelhoek, “Silicon Three-Axial Tactile Sensor,” Sensors and Actuators A: Physical, Vol. 54, No. 1-3, 1996, pp. 505-510. doi:10.1016/S0924-4247(95)01190-0 [37] M. Leineweber, G. Pelz, M. Schmidt, H. Kappert and G. Zimmer, “New Tactile Sensor Chip with Silicone Rubber Cover,” Sensors and Actuators A: Physical, Vol. 84, No. 3, 2000, pp. 236-245. doi:10.1016/S0924-4247(00)00310-1 [38] Y.-J. Yang, M.-Y. Cheng, W.-Y. Chang, L.-C. Tsao, S.-A. Yang, W.-P. Shih, F.-Y. Chang, S.-H. Chang and K.-C. Fang, “An Integrated Flexible Temperature and Tactile Sensing Array Using PI-Copper Films,” Sensors and Actuators A: Physical, Vol. 143, No. 1, 2008, pp. 143-153. doi:10.1016/j.sna.2007.10.077 [39] R. H. LaMotte and M. A. Srinivasan, “Tactile Discrimination of Shape: Responses of Slowly Adapting Mechanoreceptive Afferents to a Step Stroked across the Monkey Fingerpad,” Journal of Neuroscience, Vol. 7, No. 6, 1987, pp. 1655-1671. [40] R. H. LaMotte and M. A. Srinivasan, “Tactile Discrimination of Shape: Responses of Rapidly Adapting Mechanoreceptive Afferents to a Step Stroked across the Monkey Fingerpad,” Journal of Neuroscience, Vol. 7, No. 6, 1987, pp. 1672-1681.