1. Design of an Energy Storing Orthosis for Providing Gait to People with Spinal Cord Injury
Kyle Boughner
May 20, 2014

2. Agenda Project overview ESO concept Previous ESO device
Project objective
ESO design
ESO evaluation
ESO next steps
Conclusion

3. Project Overview Spinal Cord Injury (SCI)
Damage to any part of the spinal cord or nerves at the end of the spinal canal [1]
Often causes permanent changes in strength, sensation and other body functions below the site of the injury
Incidence in U.S. [2]
40 cases/million
12,000 new cases each year
Prevalence in U.S.
270,000 people with SCI in 2012
Severity
Quadriplegia
Paraplegia
Need
51% of SCI subjects identified gait restoration as a first choice in technology application [3]
Physical and psychological health benefits [4]
Incidence: It is estimated that the annual incidence of spinal
cord injury (SCI), not including those who die at the scene of
the accident, is approximately 40 cases per million population in
the U. S. or approximately 12,000 new cases each year. Since
there have not been any incidence studies of SCI in the U.S.
since the 1990's it is not known if incidence has changed in
recent years.
Prevalence: The number of people in the United States who
are alive in 2012 who have SCI has been estimated to be
approximately 270,000 persons, with a range of 236,000 to
327,000 persons. Note: Incidence and prevalence statistics are
estimates obtained from several studies. These statistics are not
derived from the National SCI Database.
[1] Mayo Clinic [2] NSCISC [3] Brown-Triolo et al [4] Axelson et al. 1987

4. Project Overview: Gait Restoration Technologies
Powered orthosis [2]
Passive orthosis[1]
Functional electrical stimulation (FES)
Hybrid orthotic systems [3]
Powered Orthotic Systems
Power generated external to the user
Large and heavy
Requires the user to be near the power source (tethered) or have limited operational time (system has energy storage)
Passive Orthotic Systems
Rigid system
Slow and high exertion
FES-aided Systems
application of electrical stimulation to muscle deprived of nervous control
Each muscle group utilized requires electrodes to complete FES
Electrode placement can be time consuming and inconsistent
Inconsistent placement leads to inconsistent muscle output and unpredictable system behavior
Fewer FES channels are better
Hybrid Orthotic Systems
Gait achieved with power generated by the user
Power can be generated by functional electrical stimulation (FES)
FES can be applied to multiple muscle groups to restore gait
FES is energy source, orthosis provides mechanical support and guidance, reduces demand on e-stim for support
Technology is still in primitive stage, such devices are not yet commercialized and much needs to be done before they are accepted by end users
[1] [2] Vanderbilt University [3] Goldfarb et al. 2003

5. ESO Concept Energy storage orthosis (ESO) Single channel FES
Stimulation of quadriceps
53 Nm of quadriceps torque available [1]
Four phases of gait:
Leg kinematics [2],[3]
Joint gravity torque
Joint range of motion
Gait sequence
[1] Hausdorff et al [2] Biomechanics and Motor Control of Human Movement [3] Drillis et al. 1964

6. Previous ESO Device 1st generation [1] 2nd generation [2]
Gas spring and pneumatic energy storage
Energy storage systems
Leg model testing
2nd generation [2]
Joint locking
Elastomer energy storing elements
2nd generation continued [3]
Energy element mounting location study
Device issues
Energy storing elements
Packaging
Sitting
Donning and doffing device
2nd generation ESO
2nd generation knee joint
Incidence: It is estimated that the annual incidence of spinal
cord injury (SCI), not including those who die at the scene of
the accident, is approximately 40 cases per million population in
the U. S. or approximately 12,000 new cases each year. Since
there have not been any incidence studies of SCI in the U.S.
since the 1990's it is not known if incidence has changed in
recent years.
Prevalence: The number of people in the United States who
are alive in 2012 who have SCI has been estimated to be
approximately 270,000 persons, with a range of 236,000 to
327,000 persons. Note: Incidence and prevalence statistics are
estimates obtained from several studies. These statistics are not
derived from the National SCI Database.
2nd generation ESO
2nd generation hip joint
[1] Rivard et al [2] Kangude et al [3] Kangude et al. 2010

7. Project Objective: Design and Assess ESO Thigh Concept
ESO mechanical components
Energy storing elements:
Knee equilibrium
Hip equilibrium
Hip extension transfer
Joint locking
All located on thigh (bracing above and below)
Design requirements
ESO mechanical components
No.
ESO Design Specifications
Metric
Unit
Value 1
Lateral width m
<0.54 2
Seated joint angle hip
Seated joint angle knee
Deg
105F
90F 3
Holding torque: hip and knee Nm
>31 4
Equilibrium torque hip
Equilibrium torque knee
>7.5
>8.2 5
Thigh segment weight kg
<4.34
Gait phases

8. ESO Design ESO structure Energy storing components Joint locking
Constant force springs
Joint locking
Wrap spring brakes
Three subsystems
Hip joint
Thigh segment
Support rods
Component housing
Knee joint
Right leg ESO thigh structure

9. ESO Design: Spring Selection
Two types of springs
F = Kx
Coil springs, wave springs, rubber bands
Constant force springs
Gas springs, constant force springs
Constant force springs packaging advantage
Constant force spring attachment

10. ESO Design: Joint Lock Selection
Wrap springs, friction brakes, serrated plates, dog clutches, pin locks
Advantages of wrap springs
Power failure
Fast response
Small actuation force under load
Holding torque to weight ratio
Servo motor actuation
Wrap spring brake
Serrated locking plate
Pin lock
Friction plates

11. ESO Design: Hip Joint Hip joint Hip joint wrap spring brake
Minimize width, profile, weight
Hip joint wrap spring brake
Need to lock joint in flexion and extension directions
Two wrap spring brakes
Gears to transfer shaft motion
Minimize gear width
wrap springs parallel to thigh
no added width
Hip joint
Hip joint WSB

12. ESO Design: Knee Joint Knee joint Similar to hip joint One wrap spring
Only need locking in flexion direction
Knee joint

13. ESO Evaluation: Objectives and Methods
Dynamic simulations
ESO concept capable of completing gait phases
Approximate timing of phases
Quadriceps torque needed for knee extension
Bench-top testing
ESO prototype feasibility of accomplishing gait
Timing to complete phases
Prototype design requirements
Matching predicted static joint torque
Matching predicted simulation dynamics
Evaluation methods
SimMechanics simulations
Three phases: (a) knee extension, (b) hip extension, (c) return to equilibrium
Block diagrams modeling physical system
Component parameters defined
Spring location, spring force, range of motion, quadriceps torque (15 Nm)
Force gage to measure static torque
(Wagner Instruments, Force Five)
Motion capture system for dynamic analysis
Basler camera, Pylon Viewer video recording, and MaxTRAQ motion analysis software
ESO thigh prototype
Say number of trials
Motion capture analysis
Bench-top prototype

14. ESO Evaluation: Design and Static Torque Results
No.
ESO Design Specifications
Metric
Unit
Required
Measured 1
Lateral width m
<0.54
0.505 2
Seated join angle hip
Seated joint angle knee
Deg
105F
90F
105 90 3
Holding torque: hip and knee Nm
>31 40 4
Equilibrium torque hip
Equilibrium torque knee
>7.5
>8.2 20 16 5
Thigh segment weight kg
<4.34
2.33
Prototype design requirements
Met by ESO bench-top prototype and computer solid model
Static joint torque
Energy storing springs can hold hip and knee joints are any angle in joint range of motion
Higher torque than expected towards extension
slower knee extension time than predicted

15. ESO Evaluation: Dynamic Results
Dynamic data collection example

16. ESO Evaluation: Dynamic Results
Dynamic testing
Knee extension
Hip extension
Return to equilibrium
Hip
Knee
Gait cycle time
Simulation: 2.74 sec.
Trials: 3.84 sec.
Knee joint bending
Knee Extension
Hip Extension
Hip Equilibrium
Knee Equilibrium
Simulation Time (s)
0.68
0.22
0.36
0.47
Avg. Trial Time (s)
0.97
0.24
0.72
Standard Deviation (s)
0.13
0.02
0.04
% Error
42.65%
8.04%
98.61%
48.67%
RMSD (deg)
11.23
0.65
2.13
5.56

17. ESO Evaluation: Dynamic Testing Discussion
ESO prototype feasible
Gait completed for three phases
Predicted vs. measured dynamic profiles similar
Gait cycle time is similar to other gait restoration devices
Simulation: 2.74 sec.
Trials: 3.84 sec.
Knee joint bending
Knee Extension
Hip Extension
Hip Equilibrium
Knee Equilibrium
Simulation Time (s)
0.68
0.22
0.36
0.47
Avg. Trial Time (s)
0.97
0.24
0.72
Standard Deviation (s)
0.13
0.02
0.04
% Error
42.65%
8.04%
98.61%
48.67%
RMSD (deg)
11.23
0.65
2.13
5.56

18. ESO Next Steps ESO continuation HAT and shin stability segments
Prototype testing with non-impaired user
Prototype testing with SCI user
ESO packaging and weight design
Product development
ESO product rendering

19. Conclusion: ESO Design is Feasible
Constant force springs accomplish the storing and releasing of the quadriceps torque better than other energy storing components
Wrap spring brakes lock and unlock the hip and knee joints
ESO prototype meets design criteria for functionality and requirements
Static torque measurements show that the constant force springs torque is greater than the joint gravity torque
Dynamic results show that the constant force springs do not overexert the quadriceps muscle
Dynamic simulations and testing demonstrate that the design accomplishes the gait phases
The simulation appears to predict the prototype angle profiles
Gait cycle time for ESO design is comparable to other gait restoration devices

21. Extra slides

26. Hip
Support bar
Thip
Tknee
Fsupport

28. Knee joint force vs. knee angle
Knee angle (deg) 5 10 15 20 25 30 35 40 45 50 55 60
Knee force (N)
Trial 1
57.8
47.2
43.1
40.0
36.5
33.4
29.8
25.4
20.9
22.2
15.1
8.9
2.7
Trail 2
45.4
44.0
37.4
32.5
31.6
24.9
20.0
16.5
12.5
8.0
Trial 3
57.4
54.7
43.6
38.3
36.9
33.8
25.8
21.8
17.3
12.9

29. Hip joint force vs. knee angle
Hip angle (deg)
-10 -5 5 10 15 20 25
Hip force (N)
Trial 1 48 46 37 27 12
4.4
Trail 2 42 38 29 22 18 8
Trial 3 49 47 39 19
7.6

38. No.
Purchasing Company
Description
Size
Quantity
Cost
Total 1
Online Metals
Aluminum 6061-T6 Bare Drawn Tube
0.375"x 0.049"x 0.277", 60" Length
$15.75 2
Aluminum 6061-T6511 Bare Extruded Round
0.5", 36" Length
$2.97
$18.72 3
Aluminum 6061-T6511 Bare Extruded Rectangle
0.5"x 2", 36" Length
$15.87
$34.59 4
McMaster-Carr
Sure-Grip Cushioned Loop Clamp, Aluminum
0.375" Dia. Pack of 5
$5.53
$40.12 5
Two-Piece Clamp-on Shaft Collar, Aluminum
0.375" Dia. 10
$48.50
$88.62 6
Highly Corrosion-Resistant 6063 Aluminum Square Tube
0.125"x 0.75"x 0.75", 36" Length
$7.89
$96.51 7
White Delrin Rod
2" Dia., 12" Length
$16.69
$113.20 8
Plastic Dowel Pin
0.25" Dia., 0.75" Length Pack of 50
$3.37
$116.57 9
Alloy Steel Dowel Pin
0.25" Dia., 0.75" Length Pack of 25
$5.24
$121.81
Amazon
Velcro Velstretch Strap
1x27 in 2-pack black
$22.96
$144.77 11
Constant-Force Springs
$55.74
$200.51 12
PTFE/Oil-Lubricated SAE 841 Bronze Flanged Sleeve Bearings
$15.20
$215.71 13
Alloy Steel Socket Head Cap Screws
$7.58
$223.29 14
Alloy Steel Flat-Head Socket Cap Screws
$8.29
$231.58 15
SDP/SI
Aluminum Alloy Gear
24 D.P., 45 Teeth, 20° Pressure Angle,AGMA Q10 Quality
$61.72
$293.30