1. Anti-Rollback & Brake Assist
Device for Manual Wheelchair
Problem Statement
When users of manual wheelchairs are required to traverse an incline, the wheelchair tends to roll backwards as they adjust their grip on the wheels, thus impeding forward motion.
Similarly, when traversing a decline, users do not have the ability to steer or slow their speed without endangering their hands. In both scenarios, users that may otherwise be independently mobile would require an aid.
System Diagram
Rotor
Ratchet
Wheel lock
Shaft
Bearing Blocks
Rotor Mount
Pawls (3)
Engineering Requirements
Tooth Analysis
Load set: Ratchet Stress von Mises (WCS) (psi)
Above illustrates the maximum loading scenario (41.4 lbf) applied to the face of the tooth. Assuming only 1 pawl is engaged, the system will not fail nor yield.
Importance
Function
Engineering Requirements
Status 9
Movement
Force exerted by user to hold position on incline
Pass
Grip force exerted by user to brake on decline
Wheelchair will rollback <= 0.5" when engaged
Fail 1
Independent braking inputs 3
Portability
Increase of wheelchair width when in use
Component interference when wheelchair is folded
Total system weight
Maintainability
Designed test life
COTS components
Total system cost
Number of models that system can interface
Maximum static user weight
Time to revert to original configuration
Shaft Analysis
Testing
The test fixture to the left was used to evaluate wear patterns of the pawls as the ratchet rotates past them. This simulates an engaged system on an actual wheelchair. Rotations were counted using an encoder disc and IR sensor mounted to a plate on the motor. A LabView VI recorded the data from the sensor.
The Design Chart to the left displays potential shaft materials and their respective factor of safety as a function of shaft diameter. The chosen material, 4140PH in blue with associated trend line has a factor of safety greater than the desired 1.3 bold line for all diameters above 0.44 in.
Alpha Prototype
Beta Prototype
Team 15007
~7 lbs
Weight reduction
Adaptable
Fully revertible
3 pawl design
Team 14007
~22 lbs
Maintain quick-release functionality by adding a pin in shaft
Review design to reduce variation in size and length of fasteners
Weight reduction through component design
Material selection
Alert system to ensure client is aware of system reaching end of life
Future Recommendations
Senior Design Team P15007 Members:
Jessica Jeffrey (ISE) Jacob McCarthy (ME) Warren Roser (ME) John Sweet (ME)
Faculty Guide: Edward Hanzlik Customer: Dr. Elizabeth DeBartolo, Jack Cholette
Acknowledgements: Jan Maneti, John Bonzo, Rob Kraynik