Sitting Position Monitor

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Sitting Position Monitor
If ones posture is upright, one has no need to
fear a crooked shadow. Ancient Chinese Proverb

• Group 6
• Progress Report
• Presented by Brian Loyal
• 3/23/05

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A Need for Posture Measurement
Posture Monitor gt Introduction

• More than 44,000 cases of back pain annually 1
• Observing spinal position is important for
  studying sitting posture 2
• Current methods are
• Qualitative
• Awkward for the workplace
• Short-Term
• Expensive

Source Applied Somatics

• U.S. Bureau of Labor Statistics
• Norton, et al. Differences in Measurements of
  Lumbar Curvature Related to Gender and Low Back
  Pain,
• Journal of Orthopaedic Sports Physical
  Therapy, 2004, vol. 34, 9 524-532

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General Specifications
Posture Monitor gt Introduction

• Device must quantitatively record the
  three-dimensional configuration of a subjects
  spine during his/her normal office workday

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Project Modules
Posture Monitor gt Introduction

• Data Acquisition
• How do we measure position?
• Data Handling
• How do we process information?
• Device Application
• How do we attach the devices to a subject?

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Data Acquisition

• Translating physical posture into quantitative
  information

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Acquisition Design Constraints
Posture Monitor gt Data Acquisition

• Ergonomics
• Must not interfere with subjects normal sitting
  posture
• Extend lt 1cm from skin surface
• Accuracy
• Angular measurements within 5
• Repeatable results with different operators
• Environmental Feasibility
• Signal interference
• Subject dress
• Recording length gt 4 hours

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Acquisition Options
Posture Monitor gt Data Acquisition

• 3-D Telemetry
• Electromagnetic (EM) Telemetry
• Sonic Telemetry
• Goniometry
• Optical Sensor
• Strain Sensor
• Rotary Sensor
• Other Sensors
• Digital Video Analysis
• Qualitative Strain Sensor

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Telemetry Types
Posture Monitor gt Data Acquisition gt Telemetry

• Electromagnetic
• Flock of Birds (Ascension Technologies) 4
• PRO Accuracy, low encumbrance, existing product,
  range of motion
• CON Tall sensor profile, Cost, environmental
  interference
• Sonic
• Lincoln Laboratory Wand 5
• PRO Large range of motion, lower cost
• CON Tall sensor profile, environmental
  interference, lower sampling frequency

Source Ascension Technologies
4. Flock of Birds Six Degrees-of-Freedom
Measurement Device, Ascension Technology
Corportation, Burlington, VT 5. Roberts, LG, The
Lincoln Wand, Lincoln Laboratory, Massachusetts
Institute of Technology, 2001
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Goniometer Types
Posture Monitor gt Data Acquisition gt Goniometry

• Optical Sensors
• Shape Tape (Measurand, Inc.)
• Specially treated fiber optic lines linearly
  occlude light when bent 7,8,9
• PRO Accuracy, workplace integration, low profile
• CON Restricted motion, attachment sensitivity
• Strain Sensors
• Compares length changes between inner and outer
  sides of curve 10
• PRO Robust, low price, existing product
• CON Lower accuracy, attachment sensitivity
• Rotary Sensors
• Series of rotary transducers
• Arranged like bicycle chain
• PRO Simple technology, ease-of-use, accuracy
• CON New application, higher profile, mechanical
  maintenance

Source Measurand, Inc.
Source Biometrics, Ltd.
Source Lucas Schaevitz Sensors
7. Danisch, L, et al, Spatially continuous six
degree of freedom position and orientation
sensor, Measurand, Inc., 8. United States Patent
5,633,494. 9. United States Patent
5,321,257 10. Snijders, CJ, et al, Continuous
measurements of spine movements in normal working
situations over periods of 8 hours or more,
Ergonomics, 1987, vol30, 4 639-653.
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Other Sensors
Posture Monitor gt Data Acquisition gt Other

• Digital Video Analysis
• Precision Position Tracker (WorldViz)
• Digital camera tracks positions of LED indicators
• PRO Very low profile, accurate, existing product
• CON Line-of-sight, cost, extensive space
  requirements

Source WorldViz
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Other Sensors
Posture Monitor gt Data Acquisition gt Other

• Qualitative Strain Sensor 11, 12
• Dye-treated elastomer applied to subjects back
• Position shifts cause strain in polymer,
  activates dye
• Dye pattern optically scanned and analyzed for
  posture distribution
• PRO Ease-of-use, no electronics, very little
  on-site equipment
• CON Qualitative, requires extensive analysis,
  possible allergic reactions

• Crenshaw, B, Weder, C, Deformation-Induced Color
  Changes in Melt-Processed
• Photoluminescent Polymer Blends, Chem. Mater.,
  2003, 15 4717-4724
• 12. United States Patent Application 60/390,627
  (2002)

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Acquisition Pugh Chart
Posture Monitor gt Data Acquisition
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Data Handling

• Moving, Processing, and Storing Information

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Design Constraints
Posture Monitor gt Information Handling

• Transfer Rate
• Each data stamp
• three 64 bit doubles
• Each time stamp
• one 32 bit integer
• 2.24 Kbps
• required transfer rate
• Storage Size
• 8 Mb required
• storage space

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Data Interface Options
Posture Monitor gt Information Handling
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Data Storage Options
Posture Monitor gt Information Handling
Iomega USB Hard Drive
Memorex Flash Drive
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Data Handling Components
Posture Monitor gt Information Handling

• All data interface and storage options exceed
  specifications
• Choose simplest, most robust options
• Serial RS-232
• USB Flash Drive

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Device Application

• Attaching Device Components to the Subject

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Application Constraints
Posture Monitor gt Device Application

• Strength
• Must hold device in precise position for entire
  workday
• Safety
• Must not damage skin, clothing, or other
  surrounding materials
• Ease-of-Use
• Simple to apply and remove

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Application Options
Posture Monitor gt Device Application

• Medical Adhesives
• Variety of strengths
• PRO Strong hold, direct device contact with
  skin, full range-of-motion
• CON Possible allergic reactions, skin damage,
  slow application and removal
• Self-Adhesive Tape
• PRO Simple, fast application and removal, low
  price
• CON Lower strength
• Non-Adhesive Fabrics
• Lycra garments
• PRO Easy to apply and remove, comfortable
• CON Restriction of motion, flexible device
  position, higher cost

Source Smith Nephew
Source 3M
Source Magic Marine
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Application Pugh Chart
Posture Monitor gt Device Application
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Device Overview

• Sitting Position Monitor

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Combined Components
Posture Monitor gt Device Overview
Analog signal
Analog to Digital Converter
3D coordinates via serial RS-232
Optical Goniometer
External Flash Drive
Lycra Harness
Image Source Spine Universe.com
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Technology Detail
Posture Monitor gt Device Overview gt Technology
Detail

• Refractive Index
• Measure of how fast light can travel through a
  material
• Core
• High refractive index
• Cladding
• Low Refractive Index

Fiber optic cross-section
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Optical Bend Sensors
Posture Monitor gt Device Overview gt Technology
Detail

• Light reflected below the incidence angle remains
  in the fiber
• Bending the fiber increases the incidence angle
  13
• Some light absorbed
• Fibers are treated on one side 14
• Abrasion, embossing, heat treatment, etc.
• Increased light loss
• Improves sensor sensitivity and directionality

Source efunda.com
Source Modified from Measurand, Inc.
13. Udd, E, An Overview of Fiber Optic Sensors,
Rev. Sci. Instruments, 1995, vol 66, 8
4015-4030 14. United States Patent 5,633,494.
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Shape Tape Data Acquisition
Posture Monitor gt Device Overview gt Existing
Product

• Curve represented by unit orthogonal vectors U,
  N, B
• Rotation about U and B represents ribbon bend and
  twist
• These orientations converted to Cartesian
  coordinates

Source Measurand, Inc.
Source Measurand, Inc.
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Shape Tape Limitations
Posture Monitor gt Device Overview gt Existing
Product

• Accuracy problems when poorly applied 15
• Off-angle measurements can skew the data too
  large
• Inflexible
• Fibers laminated to a ribbon of spring steel
• Holds shape but difficult to move

• Morin, E, Reid, S, The Validation of Measurand
  Shape Tape for Measuring Joint Angles,
• Proceedings, Can. Med. Biol. Eng. Conf., Nov.
  2002.

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Project Direction
Posture Monitor gt Device Overview

• Explore other materials for optical sensor
  housing
• Pre-position sensors and connections within
  garment
• Optimize design for work environment
• Casing
• Quick-Release

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Team Responsibilities
Posture Monitor gt Group Administration

• Brian Loyal
• Application Techniques
• Chris Houston
• Data Acquisition Technology
• Dave Fooshee
• Data Storage and Handling
• Webmaster
• Group
• DesignSafe
• Industry Communication

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Project Schedule
Posture Monitor gt Group Administration
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Thank You
Posture Monitor gt Group Administration

• Dr. Barbara Norton
• Washington University Department of Physical
  Therapy
• Dr. Joseph Klaesner
• Washington University Department of Biomedical
  Engineering
• Bev Stymiest
• Measurand, Inc.

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Questions?
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(No Transcript)