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

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

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] http://spinalstenosis.org 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 2012 [3] Brown-Triolo et al. 2002 [4] Axelson et al. 1987

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] http://www.aodmobility.com/home/ [2] Vanderbilt University [3] Goldfarb et al. 2003

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. 1991 [2] Biomechanics and Motor Control of Human Movement [3] Drillis et al. 1964

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. 2004 [2] Kangude et al. 2009 [3] Kangude et al. 2010

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

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

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 http://www.springmanufacturer.co.in http://www.stevensaero.com/ Constant force spring attachment www.gassprings.com

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 http://machinedesign.com http://www.jwwinco.com/ Pin lock http://www.mcmaster.com/ Friction plates http://www.energyoneclutches.com/ http://servocity.com

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

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

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

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

ESO Evaluation: Dynamic Results Dynamic data collection example

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

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

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

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

Extra slides

Hip Support bar Thip Tknee Fsupport

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

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

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