Ebo Bentil

1
ES 96 Group 2The Lever Arm

• Ebo Bentil
• Elliot Dehaan
• Frank Frisoli
• Sam Pfister
• Hollis Waite

2
Background

• Range of motion and strength are impaired in
  joint injury
• Patient diagnostics are aided by monitoring above
  limitations
• Patient rehab is aided by monitoring improvements
  in above limitations
• Rehab process is often boring and not complied to

3
Goal

• Build a physical therapy device for arm
  diagnostics and rehabilitation that will
• measure angular displacement within 3 to 5
  degrees accuracy
• provide resistance to flexion/extension motion
• attach easily to either arm
• interface with computer to monitor patients
  progress and game system for user entertainment

4
Competition

• Rubber bands
• Force providers for rehab
• non-linear resistance
• Goniometers
• measures angular displacement, similar to
  protractor
• no resistance
• Arm braces
• stabilize the joint, no resistance or angle
  measurement
• custom made and expensive
• Full system
• expensive, may be too comprehensive in diagnosis
• not used for rehab

5
Overview
Gaming System
Hand held controller

Lever Arm Output position signal
Circuitry
Computer
6
Design Requirements

• Mechanical
• Hinge
• Force provider
• Attachment to user
• Sensor attachment

• Software
• Real time feedback
• Data analysis

• Electrical
• Displacement measurement
• Velocity measurement
• Game interface
• Data acquisition

7
Hinge

• Symmetrical
• Sturdy and durable
• Easy interface with potentiometer
• Design compatibility with force packets

8
Force Provider

• Spring packets
• Range of forces
• Simple removal and adjustment
• Near constant torque for 180 degree stroke
• Variable installation position for range of
  exercises

9
Spring Packet Design
10
Attachment to User

• Lacrosse pads
• Handle grip

11
Sensor Attachment

• Attachment
• Two set screws
• Rubber
• Easily centerable

12
Displacement Measurement

• The angle through which the forearm moves is
  measured by a rotary potentiometer
• Low cost
• 360 degree range
• Resistance of a metal varies linearly with
  length. Arc length and angle subtended therefore
  directly proportional to potential difference
  across resistance

13
Velocity Measurement

• Initial considerations
• A second sensor to measure velocity
• Abandoned because it was too costly
• Take derivative of displacement signal in
  software.
• Tedious and increases the systems dependence on
  a computer
• Alternative solution differentiation circuit
• Advantages of differentiator
• Inexpensive
• Accurate
• Simplified mechanical design

14
How differentiation works .

• The basic differentiator comprises a resistor, a
  capacitor and an operational amplifier.
• Based on capacitor charging characteristic
• I CdV/dt
• I current charging capacitor, C capacitance,
• V potential difference across capacitor

R
Vin
C
Vout -RC dVin/dt
15
Game Interface
Right/Up Position corresponding to 1st threshold
VTh1
Left/Down Position corresponding to 2nd threshold
VTh2
Start/Select
Down/Left
Up/Right

• Core circuit
• 5V pulse from either comparator switches
  corresponding relay, closing the control loop on
  game controller board

Voltage divider determines threshold voltages,
VTh1 and VTh2
16
Data Acquisition

• Displacement and velocity signals input via data
  acquisition card to computer
• Labview software runs data I/O

17
Real Time Feedback Data Analysis

• Diagnostic Session
• Continuous Angle Readout
• Angular Velocity
• Maximum angular displacement
• Session analysis
• Database
• Graphs
• Game

• Rehab Session
• Continuous Angle Readout
• Angular Velocity
• Maximum angular displacement
• Session analysis
• Database
• Graphs
• Game

• Workout Session
• Continuous Angle Readout
• Angular Velocity
• Maximum angular displacement
• Session analysis
• Database
• Graphs
• Game

18
Demo
19
Prototype Materials Cost

• Stock 5
• Circuitry 10
• Springs 5
• Arm Straps 25
• Total 50

20
Improvements

• Streamline mechanical/electrical/computer design
• More force packets with higher torque
• Variable range for controller
• Attachments for legs, ankles, linear motion, etc.
  . .
• Dashpot insert for accurate force analysis
• Alternative device interfaces

21
Acknowledgements

• Many thanks
• Professor Howe
• Professor Yang
• Deke, Xuan and Joe
• ES 96 Class
• Game testers