P14042: UNA-CRUTCHRight Move, Right Place, Right Time

Subsystems Design ReviewAna AllenJoanna Dzionara-NorsenBeverly LirianoDan Sawicki

AgendaReview (Weeks 1-6)

• Background• Problem Definition• Additional Project Deliverables

Identifying Critical Subsystems• Engineering Requirements• Risk Assessment• Functional Decomposition• System Architecture

Proof Of Concept• Overview of Prototypes / Prototype Test Plan• User Feedback• Second- Order Analysis

Feasibility• Manufacturing Analysis

Detailed Design Preview (Weeks 10-12)

REVIEW (WEEKS 1-6)

Current Product

Many designs all revolving around two SEPERATE crutches.

Una-Crutch is a design that can combine from 2 separate pieces into

1 universal device

P14042 Problem Statement

Current State

• Standard axilla crutches• A prototype was developed by Kyra, but

the product is non-load bearing and has no effective connective mechanism

Desired State

• A functional product which is ergonomically friendly, has a quick and intuitive method of connection, and can be marketed to companies

Project Goals

• Perform analysis of standard axilla crutches, crutch patents, and assistive technologies used specifically for lower body injuries

Constraints• Consider Intellectual Property for the

connective mechanism

Additional Project Deliverables

Functional prototype which will be targeted

towards the majority of crutch users and will be

available as a household item.

The product will have an aesthetic

appeal and will have the potential

to be manufactured

right away.

Patent Documentation• Logbook• Prove the concept –

prototyping• Protection of

Intellectual Property• Conduction of

market research

Prototypes Introduced Week 6A B C

D E F

IDENTIFYING CRITICAL SUBSYSTEMS

Risk Assessment

Identifying Critical Sub Systems

Risk Assessment

Connective Mechanism Failure

User treats crutch as toy

User Cannot connect the crutches while immobilized on one leg

Functional Decomposition

Support independent user with lower extremity injury walking

from point A to point B in multiple types of environments.

Position Crutches

Access crutch

assembly

Permit height

adjustment

Permit connective versatility

Transport User

Support user weight

Maintain contact with the ground

Stabilize user in vertical position

Mobilizes user

Release UserDisengage from

crutch-user interface

Identifying Critical Sub Systems

Risk Assessment

Connective Mechanism Failure

User treats crutch as toy

User Cannot connect the crutches while immobilized on one leg

Engineering Requirements

Identifying Critical Sub Systems

Risk Assessment

Connective Mechanism Failure

User treats crutch as toy

User Cannot connect the crutches while immobilized on one leg

System Architecture

Identifying Critical Sub Systems

Risk Assessment

Connective Mechanism Failure

User treats crutch as toy

User Cannot connect the crutches while immobilized on one leg

Identifying Critical Sub Systems

Risk Assessment

Connective Mechanism Failure

User treats crutch as toy

User Cannot connect the crutches while immobilized on one leg1. Connective Mechanism

Identifying Critical Sub Systems

Risk Assessment

Connective Mechanism Failure

User treats crutch as toy

User Cannot connect the crutches while immobilized on one leg1. Connective Mechanism

2. Axilla Pad/ Handles

Identifying Critical Sub Systems

Risk Assessment

Connective Mechanism Failure

User treats crutch as toy

User Cannot connect the crutches while immobilized on one leg1. Connective Mechanism

2. Axilla Pad/ Handles

3. Frame

Critical Subsystems Defined

Connective Mechanism Frame Axilla Pad/

Handles

PROOF-OF-CONCEPT

Prototypes Introduced Week 6A B C

D E F

Prototypes Introduced Week 6

REVISED

A B C

D E F

Prototype G

• Pros:• Compact Design• Usable for all ages• Stable

• Cons:• Not necessarily aesthetically

pleasing• Two separate bases• Pad is in contact with the ground

Male/female mold

Pin

Prototype H

• Pros:• Lightweight • Easy to manufacture• Sliding button connective

mechanism• Cons:

• Design resembles standard axilla crutch

Sliding button

Prototypes to CreateB C

G H2.

Fra

mes

and

Con

nect

ive

Mec

hani

sms

1. A

xilla

Pad

s an

d H

andl

es

Axilla Pads and HandlesPrototypes Created

C

B

Frames and Connective MechanismsPrototype B and C

Frames and Connective MechanismsPrototype G

G

H

Frames and Connective MechanismsPrototype H

Prototype Test Plan

User FeedbackAxilla Pads and Handles

User FeedbackAxilla Pads and Handles

User FeedbackFrames and Connective Mechanisms

Second-Order Analysis

Connective Mechanism Analysis

• Magnetic Analysis• Bike Clamp Analysis

B/C Prototype Analysis

• CAD Model• Spring Analysis• Deflection Analysis

Magnetic Analysis

Magnet to a Steel Plate Example

Magnet to Magnet Example

Two configurations:

Magnet to MagnetMagnet to Plate

Two shapes:

Square/ RectangularCylindrical/ Disk

Analyzing Grade 42 magnets

Interfacing mechanism does not unlock due to user weight.Ideal value: 3 lbs.Marginal Value: 5 lbs.

Engineering Requirement S5:

Magnetic Analysis

Magnetism Physics on a Crutch

• Pull Force: quantity required to separate two attracting magnets.• Pull Force Equations: The Lorentz Equations• Pull Force Increases as Area Increases.• Pull Force Decreases as Distance Increases.

Magnetic Analysis

Configurations AnalyzedSquare Magnets Chosen

Easier to embed in material.Proper amount of Pull Force.

Square Magnet Grouping:Length (in) 1 1 1 1 1 1 1 1 1 5 5Width (in) 0.5 0.75 1 0.5 0.75 1 0.5 0.75 1 1 1

Surface Area (in^2) 0.5 0.75 1 0.5 0.75 1 0.5 0.75 1 5 5Thickness (in) 0.1875 0.1875 0.1875 0.1875 0.1875 0.1875 0.1875 0.1875 0.1875 0.1875 0.1875

Distance Between Magnets (in) 0 0 0 0.125 0.125 0.125 0.25 0.25 0.25 0.125 0.25

Pull Force Magnet to Magnet (lb) 17.06 21.93 24.65 5.45 7.66 9.12 2.67 3.97 4.9 19.92 12.24Pull Force Magnet to Plate (lb) 17.06 21.93 24.65 3.6 5.41 6.74 1.36 2.26 3 18.71 11.06

Current Magnets in Prototypes

1 2 3 4

Magnet Overview

Prototype Design Tested

Note: If used in final design, magnets will have a small distance separating them.

Bike Clamp Analysis• Split-Ring Clamp Type Shaft Collar• Analysis:

• Torque necessary to achieve pre-load• Axial holding force of seat post collar• Hoop Tension in collar

Bike Clamp Analysis

Torque in Cap Screw• Assume:

• Cap screw is coarse pitch• Low or medium carbon• Non-permanent connection• Screw diameter = 6 mm

• Torque = 6.11 Nm

Bike Clamp Analysis

Axial Holding Force• Assume:

• Coefficient of friction = 0.61• Fx = 13,000 N

Bike Clamp Analysis

Hoop Tension• Assume:

• Collar width = 12 mm• Internal radius 6.35 mm• Internal pressure = 7.08 MPa

• Fh = 540 Pa

Cheetah Leg Connection Mechanism

Grip Connection Mechanism

CAD Model: B/C Prototype

Spring Analysis

• Analyzing Spring at Base of Crutch.• Normal Force = Spring Force• N = user load• Two Stresses on Spring:

• Torsion Shear Stress• Direct Shear Stress

N

Spring Analysis

Results

• Stress absorbed by the springs results in a large stress.

• May give user more endurance to use crutches longer.

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 462.00E+05

2.20E+05

2.40E+05

2.60E+05

2.80E+05

3.00E+05

3.20E+05

3.40E+05

3.60E+05

3.80E+05

4.00E+05

2.000

2.200

2.400

2.600

2.800

3.000

3.200

3.400

Spring Analysis w/ k=100lb/in & kw=1.25 Spring Shear Stress [lb/in^2]

Spring Displace-ment [in]

θ[deg]

Sher

a St

ress

(psi

)

Sprin

g Di

spla

cem

ent (

in)

Deflection of Cheetah Leg Base• Assume:

• Carbon fiber material• Circular cross-section

• r = 0.75in = 1.91x10-2m• R2 = 0.3 m

• Deflection = 0.08in = 0.002m

R2

M

D

P

P

P

FEASIBILITY

Manufacturing Processes

Brinkman Lab Resources

3D Printing (Connective

Mechanisms)

Water Jet (Frames)

RTV Mold (Axilla Pads/ Hand grips)

DETAILED DESIGN PREVIEW

Detailed Design Phase (Weeks 10-12)

Detailed Design Phase (Weeks 10-12)

Cost and Material Analysis (Friction Analysis)

Connective

Mechanism

Prototypes from

Brinkman Lab

Focus Group for

New Prototype

s

FEA and Detailed Design

Analysis

Bill of Materials

QUESTIONS?Thank you!

BACKUP SLIDES

Customer Requirements

Final Product Test Plan