Stance Control KneeAnkleFoot Orthosis SCKAFO

1
Stance Control Knee-Ankle-Foot Orthosis (SCKAFO)

• Group Members
• Federico Carvajal
• Saleh Taebi
• Hadi Golkarieh
• Kathryn Reilander

2
Problems with Traditional Design

• Traditional knee-ankle-foot orthoses (KAFO)
  limitations
• Inability to bend the knee
• Abnormal gait
• Increase force loads at the hip

3
Solution using Stance Control

• Stance-Control Knee-ankle-foot orthosis
• Allows the knee to bend under certain conditions
• Provide stance control when needed
• Limitations of existing designs
• Knee locks only at discrete angles
• Excessive weight
• Bulky
• Expensive

4
A new approach

• New mechanical design by T. Yakimovich, J.
  Kofman, E.D. Lemaire, The Rehabilitation
  Center (The Ottawa Hospital).
• Knee locks at any angle
• Low cost
• Light
• Slim
• Improvements needed? Control system!!

5
(No Transcript)
6
System Diagram
FSR
ADConverter
PIC18F8722
Accelerometer
Actuator
Servo Motor ON / OFF
User Interface(calibration)
Photo Sensor
7
Hardware

• Our hardware module includes the following
  components
• Power supply
• Sensing circuit (FSRs)
• Switches (ON/OFF/AUTO)
• Calibration interface (push button)
• Calibration indicators (buzzer, LED)
• Actuator

8
Hardware Control Circuit
9
Hardware Implementation

• All the circuitry (excluding the PIC and
  actuator) was implemented on one single board

10
Sensors and Actuators

• Presented By
• Saleh Taebi

11
Sensors

• Functional goal
• To determine the stage of gait cycle.
• (Stance or Swing)
• Design constraints
• Sensitivity
  Durability
• Life cycle Power
  requirement
• Cost Size
• Possible Technologies
• Force Sensing Resistors (FSRs)
• Simple Contact Switches
• Incline Sensors
• Accelerometer
• Ground Proximity Sensors

12
Force Sensing Resistors

• Force is measured by electrical property of
  resistance
• Two FSRs used Toe and Heel

13
Force Sensing Resistors

• Resistance decreases and conductivity increases
  when force is applied to FSR.
• Circuit designed to produce a linear function of
  voltage vs. force over a certain range.

14
Actuator

• Functional goal
• To switch the joint between stance
  and swing mode.
• Design constraints
• Efficiency
  Actuation force
• Power requirement
  Speed/response time
• Size, Weight, Cost
  Noise, Heat
• Possible Technologies
• DC micro-motor
• Micro-solenoid
• Custom electromagnet
• Servo Motor

15
Actuator

• Possible Designs
• Using Solenoids
• High current consumption.
• Produces heat
• Bulky
• Using digital Servo Motor
• Futaba S3150
• Slim profile
• High torque
• Fast response time

16
Microcontroller

• Presented By
• Hadi Golkarieh

17
Microcontroller

• Functional goal
• Control all data flow (Perform logic decisions)
• Design constraints
• Size, Weight, Cost
• Durability
• Programmable Memory
• Speed/response time
• High level programming language
• Possible choices
• Motorola
• PIC

18
PIC18F8722

• PIC18F8722 and HPC Explorer Board
• Price 9.47
• Temperature -40C to 125C
• Programmable memory size 128 KB
• I/O 70 pins
• Pb Free Yes

19
PIC18F8722Programming requirements

• MPLAB IDE
• C capable
• Allows off PIC simulation
• Provides libraries for all PIC series
• MPLAB ICD2
• Real-time in circuit debugging
• Burns the code into the PIC

20
PIC18F8722Process Breakdown

• A/D Conversion
• FSRs generate analog signals
• Analog signals are within 0 to 4 Volts
• A/D results in a 10 bit binary equivalent
• Calibration
• Threshold calculations
• Controlling the actuator
• Solenoid
• Servo motor
• Photo Sensor (future design)
• Error control

21
Input / Output Variables

• Input
• Modes
• ON, OFF, AUTO
• Calibration
• Push button
• FSRs
• FSR_heel
• FSR_toe
• Output
• Calibration
• Buzzer / Light
• Actuator
• Swing / Stance

22
Software logic

• Presented By
• Kathryn Reilander

23
Modes of Operation

24
Transitioning from Stance to Swing
COP (center of pressure)
25
Threshold Values

• Enable Threshold
• Release Threshold

26
Decision Structure

• Possible Scenarios
• What if current state is SWING,
• and FSR_Heel gt Enable_Threshold

? then set to STANCE mode

• What if current state is SWING,
• and FSR_Heel lt Enable_Threshold
• and FSR_Toe gt Enable_Threshold

• ? then set to STANCE mode (Climbing stairs??)

27
AUTO mode Flowchart
28
Refinements of Software Logic

• Goal
• To achieve smooth, comfortable gait.
• Possible solutions
• Addition of Accelerometer
• More complex decision structure
• Optimize threshold settings

29
Analysis

• Presented By
• Federico Carvajal

30
Average Power Consumption
The solenoid consumes 18 more power than the
servo.
31
Future developments

• This project was designed for a two term period.
• Future improvements to the design may include
• Refinement of Software algorithm
• Miniaturization of circuitry (printed PCB)
• Mechanical integration with joint design
• Possible inclusion of an accelerometer
• USB interface for parameter adjustment

32
Website

• http//www.site.uottawa.ca/7Emtaeb071/project/pro
  ject.html

References

• T. Yakimovich, J. Kofman, and E.D. Lemaire,
  Design and Evaluation of a Stance Control, IEEE
  Transactions on Neural Systems and Rehabilitation
  Engineering, vol. 14, no. 3, pp. 2333-2340, Sept.
  2006
• PICDEM HPC Explorer Board, Part Number DM183022
• MPLAB ICD 2, Part Number DV164005
  www.microchip.com/
• Interlink Individual Force Sensing Resistors
• National Ergonomic Supply Inc. www.ergo-tech.ca/
• Andrew H. Hansen, PhD Dissertation, Roll-over
  Characteristics of Human Walking with
  applications for Artificial Limbs
  Rehabilitation Engineering Research Program,
  Northwestern University, 2002

33
Thank you

• Special thanks to
• Professor Misbah Islam
• Dr. Edward Lemaire
• Terris Yakimovich and the team at the Ottawa
  Hospital
• Project TAs and Lab Technicians