P14042: UNA-CRUTCH
Right Move, Right Place, Right Time
Detailed Design Review
Ana Allen
Joanna Dzionara-Norsen
Beverly Liriano
Dan Sawicki
Agenda
Review of Preliminary Detailed Design Review
Review of Final Design
• Features of Crutch
• Materials
• Cost Analysis
Feasibility of Design
• FEA Analysis
• Buckling Analysis
Review of Test Plan
Project Plan MSD II
REVIEW FROM
PRELIMINARY DDR
Crutch A
Sliding button
• Pros:
• Lightweight
• Easy to manufacture
• Sliding button connective
mechanism
• Cons:
• Design resembles standard
axilla crutch
Crutch B
• Pros:
• Aesthetically different from
standard axilla crutch
• Pads tested during user
feedback
• Cons:
• Complicated to connect
• Hard to Manufacture
Notes from Preliminary DDR
Notes from Preliminary DDR
REVIEW OF FINAL DESIGN
Revised Features of Connective Mechanism
More Durable than Nylon
Higher Strength Material
such as Steel
Alternate Connective
Mechanism
Postponement
Bill of Materials
Bill of Materials
Axilla Pad Frame
Axilla Pad Frame Pad
Screws to connect Axilla Pad frame to shaft
Shafts
Handle Frame
Handle Frame Pad
Female Button Block
Male Button Block
Pin to connect/adjust handle frame to shaft
Screws to connect shaft to Base connection
Base Connection
Height Adjustment Shaft
Button for Height Adjustment
Tip
Brinkman Lab Parts
Bill of Materials
Bill of Materials
Axilla Pad Frame
Axilla Pad Frame Pad
Screws to connect Axilla Pad frame to shaft
Shafts
Handle Frame
Handle Frame Pad
Female Button Block
Male Button Block
Pin to connect/adjust handle frame to shaft
Screws to connect shaft to Base connection
Base Connection
Height Adjustment Shaft
Button for Height Adjustment
Tip
Bar Stock
Bill of Materials
Bill of Materials
Axilla Pad Frame
Axilla Pad Frame Pad
Screws to connect Axilla Pad frame to shaft
Shafts
Handle Frame
Handle Frame Pad
Female Button Block
Male Button Block
Pin to connect/adjust handle frame to shaft
Screws to connect shaft to Base connection
Base Connection
Height Adjustment Shaft
Button for Height Adjustment
Tip
Pins/ Screws/ Buttons
FEASIBILITY OF DESIGN
The Six Key Components of the Una-Crutch
2
1
Item Number
Part
1
Shaft
2
Axilla Pad Frame
3
Adjustment Shaft
4
Tip
5
Handle
6
Base Connection
5
6
3
4
Source
Function
Engr.
Requirement
(metric)
Unit of Measure
Marginal Value
Ideal Value
9
CR3, CR4
Minimizes deflection under maximum
user weight for any crutch configuration
(single and double)
Deflection
in
0.1
0.05
S2
9
CR3, CR4
Do not fracture or break under user
load when weight is concentrated on
one crutch or both crutches as a unit.
User Weight
lbs
200
300
215 lbs is average:
+
S3
9
User will be able to use the Una-Crutch
without compromising comfort
Comfort
scale
2
1
Based off Comfort
Pain Scale (1Best, 5-Worst)
-
S4
9
Slip
Resistance
N/A
0.75
1
+
S5
9
Connectivity
lbs
5
3
-
S6
9
Short disconnect time
Separability
seconds
30
15
-
S7
9
Crutch combination is not too heavy
Weight
lbs
<7
<5
-
S8
3
Appealing to the majority
Design Appeal
yes/no
yes
yes
+
S9
9
Adjust to fit users of varying heights
Adjustability
ft
5.2<h<5.8
4.8<h<6.4
-
CR4,
CR6,
CR12
CR8,
CR12
CR1,
CR13
CR1,
CR13
CR7
CR5,
CR6,
CR10
CR9,
CR11
High coefficient of friction on normal
surfaces
Interfacing mechanism does not unlock
due to user weight
Desired
Direction
Importance
S1
Comments/
Status
Rqmt. #
Engineering Requirements
-
Item 1: Shaft
Shaft Characteristics
Shaft Static FEA
𝐹 = 0 and no friction.
• Material: 1060 Al Alloy
• Assume
• YS = 27.6 MPA
• Load at Point 1, P=150lb due to
E.R. #2.
• Constraints:
• Fixed at Point 2
• Roller at Point 1
Shaft Von Mises Stresses
Max stress < YS, Thus no failure.
Shaft Displacement
Item 2: Axilla Pad Frame
Axilla Pad Frame Characteristics
Magnets TBD
Analysis to be
completed by
Gate Review
Axilla Pad Frame Static FEA
𝐹 = 0 and no friction.
• Material: Nylon 6/10.
• Assume
• YS = 139 MPA
• Distributed load of P=300 lb
split across surface 1 due to
E.R. #2.
• Constraints:
• Fixed at Holes 2 and 3.
Axilla Pad Frame Von Mises Stresses
Max stress < YS, Thus no failure.
Axilla Pad Frame Displacement
Item 3: Adjustment Shaft
Adjustment Shaft Frame Characteristics
Adjustment Shaft Static FEA
• Assume
𝐹 = 0 and no
friction.
• Material: Al 1060.
• YS = 27 MPA
• Distributed load of P=300 lb
at hole 1 due to E.R. #2.
• Constraints:
• Roller at Surface 2.
• Fixed at Surface 3.
Adjustment Shaft Von Mises Stresses
Max stress < YS, Thus no failure.
Adjustment Shaft Displacement
Item 4: Tip
Tip Characteristics
Note: FEA Analysis neglected for Tip since part rests on Adjustment Shaft
Item 5: Handle
Handle Characteristics
Handle Static FEA
• Assume
𝐹 = 0 and no
friction.
• Material: Nylon 6/10.
• YS = 139 MPA
• Distributed load of P=300
lb along Surface 1 due to
E.R. #2.
• Constraints:
• Fixed at Shaft Surface 2.
• Roller at Shaft Surface 3.
Handle Von Mises Stresses
Max stress < YS, Thus no failure.
Handle Displacement
Item#6 Base Connection
Base Connection Characteristics
Base Connection Analyses 3
• Material: Nylon 6/10.
• YS = 139 MPA
• Constraints location 1,1a, and 2
are fixed
• Load of 300lb were places
locations 3 and 3a
1
1a
2
3a
Base Connection Von Mises Stresses
Max stress < YS, Thus no failure.
Base Connection Displacement
Buckling
• Components and Materials:
• Shafts: Aluminum
• Base Connection: Nylon 6/10
• Adjustment Shaft: Aluminum
• Assumptions:
• Half round cross-section and half round hollow cross-section
• Pin-pin
• Use Euler formula:
Buckling Results
• For no buckling to occur, load applied must be less than
the critical load
• Shafts:
Load Applied (lb)
Critical Load (lb)
Buckle? Yes/No
150
283
No
Load Applied (lb)
Critical Load (lb)
Buckle? Yes/No
300
334
No
Load Applied (lb)
Critical Load (lb)
Buckle? Yes/No
300
1641
No
• Base Connection:
• Adjustment Shaft:
PROJECT PLAN
Gate Review
Updated
BOM
Further
Review
of Axilla
Pads
• Magnet
Analysis
• Material
Revised
Handle
Frame
Cost
Analysis
Further
Review
of
Failure
Modes
MSD II Project Plan
Task Name
Duration
Subsystem Level Prep/Build
11 days
Subsystem Level Build/Test
15 days
Subsystem & System Level Build/Test/Integrate 14 days
System Level Build/Test/Integrate
16 days
Verification & Validation
16 days
Innovation
Challenge
Grant
Application
CAD Design
and Analysis
of Alternate
Connective
Mechanism
Prototype of
Alternate
Connective
Mechanism
Start
Finish
Mon 1/27/14
Tue 2/11/14
Tue 3/4/14
Mon 3/24/14
Tue 4/22/14
Mon 2/10/14
Mon 3/3/14
Fri 3/21/14
Mon 4/14/14
Tue 5/13/14
Prototype of
Crutch A
User
Feedback of
Altered
Connective
Mechanism
and Crutch A
Prototype
QUESTIONS?
Thank you everyone!
BACK UP SLIDES
Source
Function
Engr.
Requirement
(metric)
Unit of Measure
Marginal Value
Ideal Value
9
CR3, CR4
Minimizes deflection under maximum
user weight for any crutch configuration
(single and double)
Deflection
in
0.1
0.05
S2
9
CR3, CR4
Do not fracture or break under user
load when weight is concentrated on
one crutch or both crutches as a unit.
User Weight
lbs
200
300
215 lbs is average:
+
S3
9
User will be able to use the Una-Crutch
without compromising comfort
Comfort
scale
2
1
Based off Comfort
Pain Scale (1Best, 5-Worst)
-
S4
9
Slip
Resistance
N/A
0.75
1
+
S5
9
Connectivity
lbs
5
3
-
S6
9
Short disconnect time
Separability
seconds
30
15
-
S7
9
Crutch combination is not too heavy
Weight
lbs
<7
<5
-
S8
3
Appealing to the majority
Design Appeal
yes/no
yes
yes
+
S9
9
Adjust to fit users of varying heights
Adjustability
ft
5.2<h<5.8
4.8<h<6.4
-
CR4,
CR6,
CR12
CR8,
CR12
CR1,
CR13
CR1,
CR13
CR7
CR5,
CR6,
CR10
CR9,
CR11
High coefficient of friction on normal
surfaces
Interfacing mechanism does not unlock
due to user weight
Desired
Direction
Importance
S1
Comments/
Status
Rqmt. #
Engineering Requirements
-
Customer Requirements
Customer Rqmt.
#
Importance
CR1
9
Description
Comments/Status
Is adjustable to users of various heights
Comfort
CR2
9
CR3
9
Ergonomically friendly to the user
A single crutch can support the load of a user
Durability
CR4
9
Design product to last
CR5
3
Low cost of production is absolute
CR6
3
CR7
3
Aesthetically appealing
CR8
9
An interfacing mechanism allows for easy coupling and
uncoupling of the two independent crutches
Marketability
Versatility
Commercially marketable
CR9
9
Can be used outdoors and indoors
CR10
3
Lightweight crutch assembly
CR11
9
CR12
3
Ease of Use
Accommodate user daily functions
Intuitive assembly and disassembly
Risk Analysis
#
Risk
L
S
I
Action to Mitigate
Action to Remediate
1
Crutches (used individually
or connected) will not
support the user
2
3
6
Perform stress analysis for many different materials
Deformed crutch piece can be easily
accessed and replaced
2
Connective mechanism
failure
2
3
6
Perform stress and dynamic analysis for different load
configurations
Redesign connective mechanism
1
3
3
Simulate possible force distribution
Choose material with higher coefficient of
friction
2
2
4
Conduct surveys with multiple prototypes
Redesign including ergonomic issue
4
Crutch will lack slip
resistance on some
surfaces
Crutches will cause
discomfort to the user
5
User load will force crutch to
buckle
1
3
3
Design and computationally test the crutch with a
material with a high elastic modulus
Create a back-up design or a means of
strengthening the crutch frame
6
User treats crutch as a toy
2
2
4
High factor of safety - test crutch in all combinations
of loading
Strengthen the material
7
Handle snaps due to user
force
2
2
4
Make handle with high elastic modulus
New handle can be placed on unit
(adjustable handles will be
interchangeable)
8
The device will be too
expensive to manufacture
1
2
2
Design Una-Crutch with common manufacturing
techniques - research manufacturing
Return and reconsider to manufacturing
process analysis
9
A team member leaves the
team
1
3
3
Team communication to resolve issues
Reconsider the customer requirements and
deliverables
10
Design is not patentable
3
1
3
Patent research and brainstorming
Reconsider project deliverables
2
3
6
Conduct surveys with prototypes while standing on
one foot (simulate injury)
Reconsider product concept idea / discuss
with customer to refocus the target group
1
2
2
Reduce sharp surfaces in connective mechanism
Reconsider connective material/design
2
3
6
Test stair clearance
Redesign to accommodate small spaces
3
11
12
13
User cannot connect the
two crutches while
immobilized on one leg
User gets pinched when
connecting crutches
User does not feel
comfortable using crutch on
stairs
Prototype Test Plan
Final Model Test Plan
Final Model Test Plan (continued)
Backup Slide: Shaft Strain
Backup Slide: Axilla Pad Strain
Backup Slide: Adjustment Shaft Strain
Backup Slide: Handle Strain