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Human Posture Measurement System

Human Posture Measurement System. Team Personnel: Contact Email:. Brandon Ngai Lawrence Wong Josephine Wong ensc440-u-sense@sfu.ca . Overview. Overview of project Functional specifications System design System testing Current progress Future improvements. The Objective.

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Human Posture Measurement System

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  1. Human Posture Measurement System Team Personnel: Contact Email: Brandon Ngai Lawrence Wong Josephine Wong ensc440-u-sense@sfu.ca human posture measurement system

  2. Overview • Overview of project • Functional specifications • System design • System testing • Current progress • Future improvements human posture measurement system

  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 human posture measurement system

  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 human posture measurement system

  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 human posture measurement system

  6. Current Solutions • Similar devices are commercially-available • Data-loggers • MicroStrain Virtual Corset • Motion-capture system human posture measurement 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 human posture measurement system

  8. MicroStrain Virtual Corset • Limitations include: • High cost • $1,000US per unit • Uses specialized batteries • Limited measurement range • Reduced resolution between 85° and 90° human posture measurement system

  9. Motion-Capture System • Markers are mounted on the subject • Video cameras are used to track the markers • Requires a minimum of 3 cameras human posture measurement system

  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 human posture measurement system

  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 human posture measurement system

  12. The Device In Action human posture measurement system

  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) human posture measurement system

  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 human posture measurement system

  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 human posture measurement system

  16. System Block Diagram human posture measurement system

  17. Device Schematic human posture measurement system

  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 human posture measurement system

  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 human posture measurement system

  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 human posture measurement system

  21. Data Structure • 2 bytes per sample human posture measurement system

  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 human posture measurement system

  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 human posture measurement system

  24. Data Conversion • Angle measurements are calculated from the raw data by the computer human posture measurement system

  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 human posture measurement system

  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 human posture measurement system

  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 human posture measurement system

  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 human posture measurement 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 human posture measurement system

  30. System Testing • Need for extensive system testing to determine the accuracy and reliability of the device human posture measurement system

  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 human posture measurement system

  32. Device Characteristics human posture measurement system

  33. Device Characteristics human posture measurement system

  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 human posture measurement system

  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 human posture measurement system

  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 human posture measurement system

  37. Questions? human posture measurement system

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