MicroSense metrics 1 human posture measurement system Human Posture Measurement System Brandon Ngai Lawrence Wong Josephine Wong [email protected]

human posture measurement systemhuman posture measurement system

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Human Posture Human Posture Measurement SystemMeasurement System

Brandon NgaiBrandon NgaiLawrence WongLawrence WongJosephine WongJosephine Wong

[email protected]@sfu.ca

Team Personnel:Team Personnel:

Contact Email:Contact Email:


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OverviewOverview

• Overview of projectOverview of project

• Functional specificationsFunctional specifications

• System designSystem design

• System testingSystem testing

• Current progressCurrent progress

• Future improvementsFuture improvements


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The ObjectiveThe Objective

• To develop a portable human To develop a portable human monitoring device that tracks and monitoring device that tracks and records the movement of different records the movement of different parts of the bodyparts of the body

• Should combine motion-sensing, Should combine motion-sensing, data-logging, and data-data-logging, and data-transmission capabilitiestransmission capabilities


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The MotivationThe Motivation

• Motivated by the research needs of Motivated by the research needs of Dr. Steve Robinovich (SFU) and Dr. Steve Robinovich (SFU) and Dr. David Rempel (U of California)Dr. David Rempel (U of California)

• Limited number of tools available Limited number of tools available for human movement and injury for human movement and injury prevention researchprevention research


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Intended ApplicationsIntended Applications

• Study of the loss of balance and Study of the loss of balance and falling in the elderlyfalling in the elderly– Prevention of hip-fractures and Prevention of hip-fractures and

possible life-threatening injuriespossible life-threatening injuries

• Examination of the causes of work-Examination of the causes of work-related injuries in construction related injuries in construction workersworkers– Prevention of carpal tunnel syndromePrevention of carpal tunnel syndrome


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Current SolutionsCurrent Solutions

• Similar devices are commercially-Similar devices are commercially-availableavailable– Data-loggersData-loggers

• MicroStrain Virtual CorsetMicroStrain Virtual Corset

– Motion-capture systemMotion-capture system


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MicroStrain Virtual CorsetMicroStrain Virtual Corset

• Measures the angle of inclination of Measures the angle of inclination of the trunk of the bodythe trunk of the body

• Operates at 900 Operates at 900 µAµA at 3.6V at 3.6V

• Commonly used in human Commonly used in human movement research studiesmovement research studies


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MicroStrain Virtual CorsetMicroStrain Virtual Corset

• Limitations include:Limitations include:– High costHigh cost

• $1,000US per unit$1,000US per unit

– Uses specialized batteriesUses specialized batteries– Limited measurement rangeLimited measurement range

• Reduced resolution between 85Reduced resolution between 85° and 90°° and 90°


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Motion-Capture SystemMotion-Capture System

• Markers are mounted on the Markers are mounted on the subjectsubject

• Video cameras are used to track Video cameras are used to track the markersthe markers

• Requires a minimum of 3 camerasRequires a minimum of 3 cameras


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Motion-Capture SystemMotion-Capture System

• Limitations include:Limitations include:– High costHigh cost– Difficult to transportDifficult to transport– Mostly limited to lab settingsMostly limited to lab settings– Complex software packages are Complex software packages are

required to extract the data from the required to extract the data from the video feedvideo feed


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The microSense SolutionThe microSense Solution

• Pager-sized sensor units that operate Pager-sized sensor units that operate autonomously from other unitsautonomously from other units

• Measuring the angle of inclination of a Measuring the angle of inclination of a body segment in three-dimensional body segment in three-dimensional space (with respect to gravity)space (with respect to gravity)

• Stores acquired data in internal flash Stores acquired data in internal flash memory for up to 12 daysmemory for up to 12 days

• Uploads data to a computer via USBUploads data to a computer via USB


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The Device In ActionThe Device In Action


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Functional SpecificationsFunctional Specifications

• 0.50.5 degree degree resolution resolution• Measures 360Measures 360° of rotation about ° of rotation about

the x-axis and y-axisthe x-axis and y-axis• Acquires data at 32 samples per Acquires data at 32 samples per

secondsecond• Stores up to 1 Gbit of data (12 Stores up to 1 Gbit of data (12

days)days)• Powered by 2 AA batteries (final Powered by 2 AA batteries (final

design)design)


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Device LimitationsDevice Limitations

• Insensitive to rotation about the Insensitive to rotation about the vertical axisvertical axis– Sensor measures changes in Sensor measures changes in

orientation with respect to gravityorientation with respect to gravity– Unavoidable with the chosen sensor Unavoidable with the chosen sensor

technologytechnology


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System OverviewSystem Overview

• Uses two micro-electrical system Uses two micro-electrical system (MEMS) accelerometers to measure the (MEMS) accelerometers to measure the angles of inclinationangles of inclination

• Controlled by a PIC18 microcontroller Controlled by a PIC18 microcontroller with built-in USB capabilitieswith built-in USB capabilities

• Raw data is stored in 1 Gbit flash Raw data is stored in 1 Gbit flash memory chipmemory chip

• Angle outputs are calculated by the Angle outputs are calculated by the computer terminalcomputer terminal


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System Block DiagramSystem Block Diagram

POSTURE MEASUREMENT SENSOR

INCLINATIONSENSORS

MEMS accelerometersADXL203E (8-pin LCC) x 2

FLASHMEMORY1-Gbit NAND

TC58 (TSOP-48)

MICROCONTROLLER (MCU)PIC18 (44-pin TQFP)

COMPUTERTERMINAL

with USB capabilities

BATTERY2 x AA (3V)

4-bit

15-bit(8-bit R/W address/data + 7

control bits)

with USB capabilities

4-bit(dedicated)

VOLTAGE CHARGE PUMP

3.3V LTC3204(6-pin DFN)

USB data transmission(via USB mini port)


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Device SchematicDevice Schematic


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Inclination SensorsInclination Sensors

• 2 x Analog Devices ADXL203E 2 x Analog Devices ADXL203E MEMS accelerometers MEMS accelerometers

• Mounted perpendicular to each Mounted perpendicular to each otherother

• Most sensitive when the Most sensitive when the measurement axis is perpendicular measurement axis is perpendicular to gravityto gravity


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Data AcquisitionData Acquisition

• Continuous data acquisition at 32 Continuous data acquisition at 32 samples per secondsamples per second

• Sensors provide analog outputsSensors provide analog outputs• Digitalized using the 10-bit ADC on Digitalized using the 10-bit ADC on

the PIC18 microcontrollerthe PIC18 microcontroller• Non-linear relationship between Non-linear relationship between

sensor output and angle of sensor output and angle of inclinationinclination– Calculated using arcsin functionCalculated using arcsin function


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Flash MemoryFlash Memory

• Toshiba TC58DVG20A1 1-Gbit Toshiba TC58DVG20A1 1-Gbit NAND flash memoryNAND flash memory

• Holds 128Mb of dataHolds 128Mb of data

• Durable and reliableDurable and reliable

• Interfaces with the PIC18 Interfaces with the PIC18 microcontroller via 8 address/data microcontroller via 8 address/data lines and 7 control lineslines and 7 control lines


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Data StructureData Structure

• 2 bytes per sample2 bytes per sample


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Data StorageData Storage

• A 1-Gbit chip can store up to 12 A 1-Gbit chip can store up to 12 days of data at 32 samples per days of data at 32 samples per secondsecond

• 2-Gbit NAND flash memory chips 2-Gbit NAND flash memory chips are also availableare also available– More difficult to acquireMore difficult to acquire


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Data TransmissionData Transmission

• Data is transmitted to a computer Data is transmitted to a computer via an USB cablevia an USB cable

• The computer automatically The computer automatically recognizes the sensor devicerecognizes the sensor device

• Data transmission begins at the Data transmission begins at the user’s commanduser’s command– Graphical user interfaceGraphical user interface


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Data ConversionData Conversion

• Angle measurements are Angle measurements are calculated from the raw data by the calculated from the raw data by the computercomputer


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Graphical User InterfaceGraphical User Interface

• Windows-based GUIWindows-based GUI

• Allows user to establish and Allows user to establish and terminate data communications terminate data communications with the sensor unitswith the sensor units

• Allows user to initiate data transferAllows user to initiate data transfer


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Data OutputData Output

• System outputs a comma System outputs a comma separated value (CSV) fileseparated value (CSV) file

• Lists the angles of inclination with Lists the angles of inclination with respect to the x-axis and y-axis at respect to the x-axis and y-axis at each sampling timeeach sampling time

• Readable using Microsoft ExcelReadable using Microsoft Excel


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Design ChallengesDesign Challenges

• Component identification and Component identification and acquisitionacquisition– Long shipping delaysLong shipping delays– Need for adapter boards for small Need for adapter boards for small

packagespackages

• Subdividing the systemSubdividing the system– Difficulties in integrating the system Difficulties in integrating the system

modulesmodules


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Testing ProtocolTesting Protocol

• Real-time testingReal-time testing– Used to verify sensor accuracy and Used to verify sensor accuracy and

sensor-to-microcontroller sensor-to-microcontroller communicationscommunications

• System testingSystem testing– Required to verify data storage and Required to verify data storage and

retrievalretrieval– Ensures the proper integration of the Ensures the proper integration of the

systemsystem


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Real-Time TestingReal-Time Testing

• Device is connected to a computer Device is connected to a computer via USBvia USB

• Enables sensor calibrationEnables sensor calibration

• Device outputs are compared to a Device outputs are compared to a 1-axis digital level for accuracy1-axis digital level for accuracy


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System TestingSystem Testing

• Need for extensive system testing Need for extensive system testing to determine the accuracy and to determine the accuracy and reliability of the devicereliability of the device


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Testing ChallengesTesting Challenges

• Difficult to test each system module Difficult to test each system module independently of other modulesindependently of other modules

• Heavily reliant on USB-to-PC Heavily reliant on USB-to-PC interface during testinginterface during testing

• Difficult to verify timer operationDifficult to verify timer operation

• Hard to pinpoint problems and Hard to pinpoint problems and debug the system debug the system


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Device CharacteristicsDevice Characteristics

ADXL203 Digital Characteristics for Sensor 1 X-Axis (About Y-Axis)

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0 10 20 30 40 50 60 70 80 90 100

Angle (deg)

AD

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1x

1y

2x

2y


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Device CharacteristicsDevice Characteristics

ADXL203 Digital Characteristics for Sensor 1 Y-Axis (About X-Axis)

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Angle (deg)

AD

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1y

2x

2y


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Power ConsumptionPower Consumption

• Prototype is powered by 3 AA batteriesPrototype is powered by 3 AA batteries• Standby modeStandby mode

– 13mA of current13mA of current

• Data acquisition modeData acquisition mode– 45mA of current45mA of current

• Data transmission mode (USB Data transmission mode (USB connected)connected)– 50mA of current50mA of current

• Need to minimize power consumptionNeed to minimize power consumption


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Current StatusCurrent Status

• Device can measure, record, and Device can measure, record, and transmit datatransmit data

• Can also operate in real-time mode Can also operate in real-time mode (for system testing)(for system testing)

• Currently developing a time-Currently developing a time-stamping algorithm (to synchronize stamping algorithm (to synchronize data from multiple sensors)data from multiple sensors)

• Need to test the system for Need to test the system for accuracy and reliabilityaccuracy and reliability


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Future ImprovementsFuture Improvements

• Final prototype will require 2 AA Final prototype will require 2 AA batteriesbatteries

• Users will be able to mark key Users will be able to mark key events in the data with the press of events in the data with the press of a buttona button

• May implement wireless data May implement wireless data transmissiontransmission


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Questions?Questions?

Documents

MicroSense metrics 1 human posture measurement system Human Posture Measurement System Brandon Ngai Lawrence Wong Josephine Wong [email protected]