1. P08002 Automated Parallel Bars
Jeff Osborne Ryan Hellems Justin Knowles Justin Vowles Jessica Stalker
ME ME, Lead ME ME ISE
Project Introduction
Working with the Physical Therapy clinic at Nazareth a system was developed to simplify the adjustment of their parallel bar system, which is used for neurological rehabilitation. The new design replaced the 3-independent hole-and-pin posts with one simple hand crank. The system also eliminates the hazards associated with uneven or unlevel bars, and allows for easier patient repeatability.
Entire Current System
Current System
Customer Needs/Engineering Specs
“They Said” “We Heard”
Safe for patient and PT
Ease of adjust
Accuracy
Reliability
No pinch points or sharp edges
No trip hazards
Minimal vertical deflection (≤ 1.1“ at max height)
Reasonable time to adjust (< 60 seconds)
Ease of adjustment (torque < 8.5 ft-lbs)
Ensure bar is always horizontal (+/ degrees)
Height indicator (16 in. range: in.)
Performance constant for life (288,000 cycles, 5 years)
Preservation of current system (ability to “roll back”)
Redesigned System
Design Analysis
Crank Tower Subsystem
4:1 gear ratio for belt drive provides 0.5 inch per revolution
Ergonomically located hand crank, easy to turn
Removable handle prevents incidental adjustment
System FBD
Torque to Raise
Max Horizontal Deflection, plus contact deflection: 0.43 inches
Max Von Mises
18635 psi
[modeled with no clearance]
Input force needed to raise bars with 6 inch handle and 4:1 gear ratio = 2.19 lbf
Lifting Subsystem
Deflection Test Results
Three posts tied in series by a single drive shaft
1:1 perpendicular miter gears transmit rotation from drive shaft to ACME rod
5/8-8 ACME Rod supports vertical loads, transmits weight to outer post.
ACME nut welded to inner post rides up/down rotating threaded rod
Conclusion: Inner posts were powder coated and plastic shims were added to reduce clearance and deflection.
This material is based upon work supported by the National Science Foundation under Award No. BES Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect the views of the National Science Foundation.