Textile pressure sensor design , error modeling and evaluation

This thesis presents a new textile pressure sensor that can be integrated into clothing. The sensing principle of a variable capacitor is used. Electrodes of conductive textiles are arranged on both sides of a compressible spacer. Two basic architectures are evaluated: Perpendicular stripes on both sides of a compressible spacer forming the capacitors at their crossover points and single electrodes on one side and a common electrode on the other side of the spacer. Sensors of various sizes are built with 1, 16, 30 and 240 sensing elements. The focus of this work is to model the sensor behavior to reduce error sources. By using such algorithms, the field is opened for using standard material and a simple design for the sensor. The models used can be easily adapted to other pressure sensors and even strain sensors. Errors induced by hysteresis can be reduced from 60% to below 10% by using the Preisach model. Additionally, drift effects are modeled by measuring the step response of the used textile spacer. A new model is developed, reducing drift errors below 5% for a duration of one hour. Finally, the impact of error sources such as hysteresis, drift, noise and sensor failure is researched for a concrete application: Classification of sitting postures from pressure patterns measured on a seat. The influence of the errors is simulated on the one hand and measured with the classification accuracy and the distance between the classes as measure on the other hand. It is shown that drift effects can be neglected, while modeling the hysteresis enhances the classification rate by 35%. Replacing failing sensors by the mean value of adjacent elements improves the result by 24%. The system with the textile sensor performs similarly to a commercially available pressure mat for this application when the relevant error sources are compensated. Furthermore, the sensor has shown its usefulness by measuring muscle activity and by supervising the pressure distribution in compression stockings.

[1]  Jack Chen,et al.  Towards modular integrated sensors: the development of artificial haircell sensors using efficient fabrication methods , 2003, Proceedings 2003 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS 2003) (Cat. No.03CH37453).

[2]  Billie F. Spencer,et al.  Models for hysteresis and application to structural control , 1997, Proceedings of the 1997 American Control Conference (Cat. No.97CH36041).

[3]  David G. Stork,et al.  Pattern classification, 2nd Edition , 2000 .

[4]  Fabrizio Scarpa,et al.  Passive and MR Fluid-coated Auxetic PU Foam – Mechanical, Acoustic, and Electromagnetic Properties , 2004 .

[5]  Carl André Nørstebø.  Intelligent Textiles, Soft Products , 2004 .

[6]  Douglas L. Jones,et al.  Technology development of integrated multi-modal and flexible tactile skin for robotics applications , 2003, Proceedings 2003 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS 2003) (Cat. No.03CH37453).

[7]  Markus Klann,et al.  Playing with fire: participatory design of wearable computing for fire fighters , 2007, CHI Extended Abstracts.

[8]  A. Dehe,et al.  AC transfer function of electrostatic capacitive sensors based on the 1-D equivalent model: application to silicon microphones , 2003 .

[9]  M.A.T. Sanduleanu,et al.  1GHz tuning range, low phase noise, LC oscillator with replica biasing common-mode control and quadrature outputs , 2001, Proceedings of the 27th European Solid-State Circuits Conference.

[10]  A. Dehe,et al.  Constant charge operation of capacitor sensors based on switched-current circuits , 2003 .

[11]  U.S. Ganguly.  RC-oscillator synthesis: Sub-audio-frequency generation with a single control , 1978, Proceedings of the IEEE.

[12]  Leon O. Chua,et al.  A Generalized Hysteresis Model , 1972 .

[13]  P. Cloetens,et al.  3D quantitative image analysis of open-cell nickel foams under tension and compression loading using X-ray microtomography , 2005 .

[14]  Paul Lukowicz,et al.  Detecting and Interpreting Muscle Activity with Wearable Force Sensors , 2006, Pervasive.

[15]  Xiujun Li,et al.  A novel interface circuit for grounded capacitive sensors with feedforward-based active shielding , 2008 .

[16]  G. Mesmacque,et al.  Analysis of the Viscoelastoplastic Behavior of Expanded Polystyrene under Compressive Loading: Experiments and Modeling , 2001 .

[17]  Paul Lukowicz,et al.  Wearable Activity Tracking in Car Manufacturing , 2008, IEEE Pervasive Computing.

[18]  Lucy E. Dunne,et al.  Initial development and testing of a novel foam-based pressure sensor for wearable sensing , 2005, Journal of NeuroEngineering and Rehabilitation.

[19]  L. Schwartz,et al.  A mathematical model for an expanding foam. , 2003, Journal of colloid and interface science.

[20]  Egor P. Popov,et al.  Seismic Energy Dissipators for RC Panels: Analytical Studies , 2001 .

[21]  C. Lyder,et al.  Validating the Braden Scale for the prediction of pressure ulcer risk in blacks and Latino/Hispanic elders: a pilot study. , 1998, Ostomy/wound management.

[22]  F. Preisach.  Über die magnetische Nachwirkung , 1935 .

[23]  K. Martin.  A voltage-controlled switched-capacitor relaxation oscillator , 1981, IEEE Journal of Solid-State Circuits.

[24]  D. H. Everett,et al.  A general approach to hysteresis , 1952 .

[25]  Marco Luca Sbodio,et al.  A Wearable Computing Prototype for supporting training activities in Automotive Production , 2007 .

[26]  Hong Z. Tan,et al.  A real-time sitting posture tracking system , 2000 .

[27]  D. Cottet,et al.  An investigation of the material and process parameters for thin-film MCM-D and MCM-L technologies up to 100GHz , 2003, 53rd Electronic Components and Technology Conference, 2003. Proceedings..

[28]  Elgar Fleisch,et al.  Flexible-foam-based capacitive sensor arrays for object detection at low cost , 2008 .

[29]  Pressure ulcers: assessment, prevention, and compliance. , 2002, The Case manager.

[30]  B. Barrois,et al.  A survey of pressure sore prevalence in hospitals in the greater Paris region. , 1995, Journal of wound care.

[31]  Hae-Seung Lee,et al.  Digital cancellation of noise and offset for capacitive sensors , 1993 .

[32]  K. Rajanna,et al.  Tactile sensor based on piezoelectric resonance , 2002, Proceedings of IEEE Sensors.

[33]  A. C. Jayasuriya,et al.  Pyroelectric properties of linear aromatic polyurethanes , 1996 .

[34]  Paul Lukowicz,et al.  Sensing muscle activities with body-worn sensors , 2006, International Workshop on Wearable and Implantable Body Sensor Networks (BSN'06).

[35]  Gerard C. M. Meijer,et al.  New concepts for smart signal processors and their application to PSD displacement transducers , 1992 .

[36]  F. Campi,et al.  A dynamically reconfigurable monolithic CMOS pressure sensor for smart fabric , 2003 .

[37]  David Birchfield,et al.  A pressure sensing floor for interactive media applications , 2005, ACE '05.

[38]  Massimiliano Avalle,et al.  Mechanical Models of Cellular Solids, Parameters Identification from Experimental Tests , 2005 .

[39]  F.M.L. Van der Goes,et al.  Low-Cost Smart Sensor Interfacing , 1996 .

[40]  Maurice Beck,et al.  REVIEW ARTICLE: Electronic transducers for industrial measurement of low value capacitances , 1988 .

[41]  G. Troster,et al.  Design Concept of Clothing Recognizing Back Postures , 2006, 2006 3rd IEEE/EMBS International Summer School on Medical Devices and Biosensors.

[42]  J N Morris,et al.  The epidemiology and natural history of pressure ulcers in elderly nursing home residents. , 1990, JAMA.

[43]  Alois Ferscha,et al.  Supporting Implicit Human-to-Vehicle Interaction: Driver Identification from Sitting Postures , 2008 .

[44]  Olga Vitek,et al.  Screening for pressure ulcer risk in an acute care hospital: development of a brief bedside scale. , 2002, Journal of clinical epidemiology.

[45]  V. Lumelsky,et al.  Sensitive skin , 2000, IEEE Sensors Journal.

[46]  G. Tröster,et al.  Temperature Profile Estimation with Smart Textiles , 2005 .

[47]  C. Gokcek,et al.  Tracking the resonance frequency of a series RLC circuit using a phase locked loop , 2003, Proceedings of 2003 IEEE Conference on Control Applications, 2003. CCA 2003..

[48]  I. Mayergoyz,et al.  Generalized Preisach model of hysteresis , 1988 .

[49]  Alois Ferscha,et al.  Driver Activity Recognition from Sitting Postures , 2007, Mensch & Computer Workshopband.

[50]  E. Landis,et al.  Micro-injection studies of capillary blood pressure in human skin , 1930 .

[51]  Elgar Fleisch,et al.  Weight-Sensitive Foam to Monitor Product Availability on Retail Shelves , 2007, Pervasive.

[52]  Rob Gorbet,et al.  Control of hysteretic systems with Preisach representations , 1997 .

[53]  E. Della Torre,et al.  Particle Interaction in Magnetic Recording Tapes , 1960 .

[54]  G. Troster,et al.  Design and Characterization of Purely Textile Patch Antennas , 2006, IEEE Transactions on Advanced Packaging.

[55]  Paul Lukowicz,et al.  Textile Pressure Sensor for Muscle Activity and Motion Detection , 2006, 2006 10th IEEE International Symposium on Wearable Computers.

[56]  Alex Pentland,et al.  A sensing chair using pressure distribution sensors , 2001 .

[57]  P. Binkley.  Predicting the potential of wearable technology , 2003 .

[58]  M. Shimojo,et al.  A tactile sensor sheet using pressure conductive rubber with electrical-wires stitched method , 2004, IEEE Sensors Journal.

[59]  Masayuki Inaba,et al.  Development of soft and distributed tactile sensors and the application to a humanoid robot , 2002, Adv. Robotics.

[60]  Roberto Guerrieri,et al.  A textile based capacitive pressure sensor , 2002, Proceedings of IEEE Sensors.

[61]  Z. Petrović,et al.  Novel dielectrics from IPNs derived from castor oil based polyurethanes , 1994 .

[62]  F.-Y. Chang,et al.  Design and fabrication of an artificial skin using PI-copper films , 2007, 2007 IEEE 20th International Conference on Micro Electro Mechanical Systems (MEMS).

[63]  John M. Sullivan,et al.  The Geometry of Bubbles and Foams , 1999 .

[64]  R. Wojtyna,et al.  Contribution to the linear theory of frequency stability of RC oscillators , 1986 .

[65]  Tilak Dias,et al.  Fibre-meshed transducers based real time wearable physiological information monitoring system , 2004, Eighth International Symposium on Wearable Computers.

[66]  F. N. Toth,et al.  Ultra-linear, low-cost measurement system for multi-electrode pF-range capacitors , 1995, Proceedings of 1995 IEEE Instrumentation and Measurement Technology Conference - IMTC '95.

[67]  C.M.A. Ashruf,et al.  Thin flexible pressure sensors , 2002 .

[68]  B. Stevens,et al.  Improvements in the theory and design of RC oscillators , 1971 .

[69]  J. Kittler,et al.  Feature Set Search Alborithms , 1978 .

[70]  G.C.M. Meijer,et al.  Concepts for the design of smart sensors and smart signal processors and their application to PSD displacement transducers , 1991, TRANSDUCERS '91: 1991 International Conference on Solid-State Sensors and Actuators. Digest of Technical Papers.

[71]  H. Brem,et al.  Protocol for the successful treatment of pressure ulcers. , 2004, American journal of surgery.

[72]  Andreas Krause,et al.  Robust, low-cost, non-intrusive sensing and recognition of seated postures , 2007, UIST.

[73]  Heinz Wörn,et al.  Development of a flexible tactile sensor system for a humanoid robot , 2003, Proceedings 2003 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS 2003) (Cat. No.03CH37453).

[74]  Lynne Broderick,et al.  Patterns of recurrent pressure ulcers after spinal cord injury: identification of risk and protective factors 5 or more years after onset. , 2004, Archives of physical medicine and rehabilitation.

[75]  Tomomasa Sato,et al.  Body parts positions and posture estimation system based on pressure distribution image , 1999, Proceedings 1999 IEEE International Conference on Robotics and Automation (Cat. No.99CH36288C).

[76]  R. Dutton,et al.  Minimum achievable phase noise of RC oscillators , 2005, IEEE Journal of Solid-State Circuits.

[77]  Maurice Beck,et al.  A multi-interface level measurement system using a segmented capacitance sensor for oil separators , 1994 .

[78]  W. Brown.  Failure of the Local-Field Concept for Hysteresis Calculations , 1962 .

[79]  J Tapson,et al.  Improved capacitance measurement by means of resonance locking , 1994 .

[80]  Y. Wen.  Method for Random Vibration of Hysteretic Systems , 1976 .

[81]  A. G. J. Holt,et al.  A class of RC oscillators , 1967 .