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  • 1. Human Posture Measurement System Brandon Ngai Lawrence Wong Josephine Wong [email_address] Team Personnel: Contact Email:
  • 2. Overview
    • Overview of project
    • Functional specifications
    • System design
    • System testing
    • Current progress
    • Future improvements
  • 3. The Objective
    • To develop a portable human monitoring device that tracks and records the movement of different parts of the body
    • Should combine motion-sensing, data-logging, and data-transmission capabilities
  • 4. The Motivation
    • Motivated by the research needs of Dr. Steve Robinovich (SFU) and Dr. David Rempel (U of California)
    • Limited number of tools available for human movement and injury prevention research
  • 5. Intended Applications
    • Study of the loss of balance and falling in the elderly
      • Prevention of hip-fractures and possible life-threatening injuries
    • Examination of the causes of work-related injuries in construction workers
      • Prevention of carpal tunnel syndrome
  • 6. Current Solutions
    • Similar devices are commercially-available
      • Data-loggers
        • MicroStrain Virtual Corset
      • Motion-capture system
  • 7. MicroStrain Virtual Corset
    • Measures the angle of inclination of the trunk of the body
    • Operates at 900 µA at 3.6V
    • Commonly used in human movement research studies
  • 8. MicroStrain Virtual Corset
    • Limitations include:
      • High cost
        • $1,000US per unit
      • Uses specialized batteries
      • Limited measurement range
        • Reduced resolution between 85 ° and 90°
  • 9. Motion-Capture System
    • Markers are mounted on the subject
    • Video cameras are used to track the markers
    • Requires a minimum of 3 cameras
  • 10. Motion-Capture System
    • Limitations include:
      • High cost
      • Difficult to transport
      • Mostly limited to lab settings
      • Complex software packages are required to extract the data from the video feed
  • 11. The microSense Solution
    • Pager-sized sensor units that operate autonomously from other units
    • Measuring the angle of inclination of a body segment in three-dimensional space (with respect to gravity)
    • Stores acquired data in internal flash memory for up to 12 days
    • Uploads data to a computer via USB
  • 12. The Device In Action
  • 13. Functional Specifications
    • 0.5 degree resolution
    • Measures 360 ° of rotation about the x-axis and y-axis
    • Acquires data at 32 samples per second
    • Stores up to 1 Gbit of data (12 days)
    • Powered by 2 AA batteries (final design)
  • 14. Device Limitations
    • Insensitive to rotation about the vertical axis
      • Sensor measures changes in orientation with respect to gravity
      • Unavoidable with the chosen sensor technology
  • 15. System Overview
    • Uses two micro-electrical system (MEMS) accelerometers to measure the angles of inclination
    • Controlled by a PIC18 microcontroller with built-in USB capabilities
    • Raw data is stored in 1 Gbit flash memory chip
    • Angle outputs are calculated by the computer terminal
  • 16. System Block Diagram
  • 17. Device Schematic
  • 18. Inclination Sensors
    • 2 x Analog Devices ADXL203E MEMS accelerometers
    • Mounted perpendicular to each other
    • Most sensitive when the measurement axis is perpendicular to gravity
  • 19. Data Acquisition
    • Continuous data acquisition at 32 samples per second
    • Sensors provide analog outputs
    • Digitalized using the 10-bit ADC on the PIC18 microcontroller
    • Non-linear relationship between sensor output and angle of inclination
      • Calculated using arcsin function
  • 20. Flash Memory
    • Toshiba TC58DVG20A1 1-Gbit NAND flash memory
    • Holds 128Mb of data
    • Durable and reliable
    • Interfaces with the PIC18 microcontroller via 8 address/data lines and 7 control lines
  • 21. Data Structure
    • 2 bytes per sample
  • 22. Data Storage
    • A 1-Gbit chip can store up to 12 days of data at 32 samples per second
    • 2-Gbit NAND flash memory chips are also available
      • More difficult to acquire
  • 23. Data Transmission
    • Data is transmitted to a computer via an USB cable
    • The computer automatically recognizes the sensor device
    • Data transmission begins at the user’s command
      • Graphical user interface
  • 24. Data Conversion
    • Angle measurements are calculated from the raw data by the computer
  • 25. Graphical User Interface
    • Windows-based GUI
    • Allows user to establish and terminate data communications with the sensor units
    • Allows user to initiate data transfer
  • 26. Data Output
    • System outputs a comma separated value (CSV) file
    • Lists the angles of inclination with respect to the x-axis and y-axis at each sampling time
    • Readable using Microsoft Excel
  • 27. Design Challenges
    • Component identification and acquisition
      • Long shipping delays
      • Need for adapter boards for small packages
    • Subdividing the system
      • Difficulties in integrating the system modules
  • 28. Testing Protocol
    • Real-time testing
      • Used to verify sensor accuracy and sensor-to-microcontroller communications
    • System testing
      • Required to verify data storage and retrieval
      • Ensures the proper integration of the system
  • 29. Real-Time Testing
    • Device is connected to a computer via USB
    • Enables sensor calibration
    • Device outputs are compared to a 1-axis digital level for accuracy
  • 30. System Testing
    • Need for extensive system testing to determine the accuracy and reliability of the device
  • 31. Testing Challenges
    • Difficult to test each system module independently of other modules
    • Heavily reliant on USB-to-PC interface during testing
    • Difficult to verify timer operation
    • Hard to pinpoint problems and debug the system
  • 32. Device Characteristics
  • 33. Device Characteristics
  • 34. Power Consumption
    • Prototype is powered by 3 AA batteries
    • Standby mode
      • 13mA of current
    • Data acquisition mode
      • 45mA of current
    • Data transmission mode (USB connected)
      • 50mA of current
    • Need to minimize power consumption
  • 35. Current Status
    • Device can measure, record, and transmit data
    • Can also operate in real-time mode (for system testing)
    • Currently developing a time-stamping algorithm (to synchronize data from multiple sensors)
    • Need to test the system for accuracy and reliability
  • 36. Future Improvements
    • Final prototype will require 2 AA batteries
    • Users will be able to mark key events in the data with the press of a button
    • May implement wireless data transmission
  • 37. Questions?