Muscle Force Assessment. Powered Orthotics

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1 Muscle Force Assessment Powered Orthotics William Durfee Department of Mechanical Engineering University of Minnesota Minneapolis, USA

2 April 9-11, 2013 University Hotel, UMN

3 Muscle Force Assessment

4 Why Assess Muscle Force? Loss of muscle strength links to risk of disability Muscle strength predicts survival, middle age and later Many diseases and conditions can impair muscle function Diabetes Sepsis Heart failure Immobilization Neuromuscular diseases

5 Force Assessment by E-Stim STIM MUSCULOSKELETAL SYSTEM FORCE Consistent input Isolates the muscle Patient not involved

6 Identification of intact muscle properties more challenging What you want What you have Skeletal geometry 2. Muscle in series with a springy tendon

7 Skeletal geometry u(t) STIM MUSCULOSKELETAL SYSTEM y(t) FORCE/MOTION x(t) u(t) MT f(t) GEOM τ(t) LIMB DYNAMICS θ(t) GEOM -1

8 Muscle-tendon model muscle a(t) CE L M (t) V M (t) F M (t)=f T (t)=f(t) tendon SE PE passive

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10 Preliminary ID Results

11 Testing Muscle Force in the ICU

12 Case Study Revealed Dramatic Changes in Force in Long Term Critically Ill Patients 4 years, 25 patients, 8 long-term Pts 3 & 6 did not survive, forces continually went down. Ginz, Iaizzo, Acta Anes Scand, 2008

13 Apparatus for TA Assessment Ginz, Iaizzo, Acta Anes Scand, 2008

14 Improved Devices

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16 A simple tool to measure limb inertia CE M m K SE K PE (θ) M J (θ) B PE (θ)

17 Reanimating Paralyzed Muscle for Walking Muscle-powered orthosis

18 Paralyzed Muscle Can Be Activated With Pulses of Current Brain Stimulator Spinal Cord Limb

19 Controlled Brake Orthosis Muscle stimulation provides power Brakes for locking and control Orthosis provides guidance and support

20 CBO in Operation Stimulate quadriceps for stance control High force, high energy (relatively) Stimulate reflex for stepping motion Erratic Habituates CBO controls swing, locks during stance Orthosis a mounting platform for sensors Four-subject study Goldfarb et al., IEEE TNSRE, 2003

21 Energy Storing Orthosis Release ambient (atmospheric pressure) air as hip flexes Compress air and force into accumulator as knee extends Discharge pressurized air to drive hip extension Take in ambient (atmospheric) air as knee flexes (a) (b) (c)

22 Kangude et al., IEEE EMBS Conference, 2010

23 Compressed gas drives hip

24 Non-Muscle Powered Orthoses

25 Muscle Motors

26 Power Density (W/kg) Muscle Has Unimpressive Power Density Muscle Athlete's Muscle Electric Motor Automobile Engine Vogel (2001), "Prime Mover"

27 Power Density (W/kg) Muscle 11 Athlete's Muscle 220 Electric Motor 440 Automobile Engine Aircraft Turbine Engine

28 Muscle Has Unique Features Uni-direction, short stroke (5-20%) Pull force: 30 lbs/sq. in. 25% efficient Extensive infrastructure Exquisite control Fatigues Compliant, back-drivable Clean Cool Quiet! Vogel (2001), "Prime Mover"

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30 Hydraulics Are Small Electric Motor Hydraulic Pump Parker 108 Series Pump

31 275,000 pounds!

32 Fearless Operator Control

33 Fluid Power Is Good For Human Scale Applications High force-to-weight High power-to-weight High force-to-volume Transport pressurized fluid through flexible hoses

34 Fluid Power Is Bad For Human Scale Applications As size down, friction losses in cylinders and drag losses in hoses goes up Oil is messy Tiny, high-pressure components do not exist

35 Replacing Muscle With Fluid Power

36 Challenges Power supply Actuators Packaging Control Ironman, 2008

37 Vision: Wearable fluid power in the 10 to 100 W range

38 Power (W) Ankle Power, 85 Kg Person Walking 200 Peak ~200 W Average ~13 W Gait Cycle (%) 85 Kg person walking (Winters: Biomechanics of Human Motion)

39 Pneumatic Ankle Foot Orthosis

40 Ankle Power (W/kg) Ankle Moment (Nm/kg) Pneumatic Portable Powered AFO 20 ounce CO 2 bottle Belt Worn CO 2 (100psi) Onboard Electronics 0.2 2,000 steps ISubPF Right Ankle Moment and Power 0.1 Pressure regulator Sensors: Rotary and Pressure Restored toe-off push Shoes AFO Assist -0.2 Shorter et al., JRRD, % Gait Cycle

41 For Pneumatics, Get Rid of the Battery

42 MJ/Kg Energy Density NiMh Lith Ion Methanol Efficiency Motor-Battery: 75% Fuel-Engine: 5% Fuel needed Batt:.09 MJ = 0.15 Kg Engine: 1.4 MJ =.007 Kg

43 W/Kg Power Density Need 20 W Electric: 0.13 Kg 4-stroke: 0.08 Kg 2-stroke: 0.01 Kg

44 Create Compressed Air With an IC Engine Goal High efficiency air compressor that delivers 50 W of cold compressed air Approach Free-piston, 2-stroke, HCCI combustion engine with coupled compressor Advantages More compact than battery + motor Easier to fabricate than micro-turbine Challenges Miniaturization Regulating piston motion

45 Comp block First Prototype Engine block Silencer Engine cylinder head Engine liner Engine piston Reed valve 5 Rebound spring Con-rod set Center plate Carburetor Comp piston (pin) Compressor liner Yes, it is noisy, smelly, hot

46 TINY HYDRAULICS Research Question Does the power and force density advantage of hydraulics apply for tiny systems? Design Question When will a hydraulic system be lighter than an electromechanical system? Pneumatics has limits Low pressure High compliance As size goes down, friction, losses go up Target 10 to 100 W range Tiny hydraulic components do not exist Systems approach drives design

47 System Analysis Approach 1. Develop simple, static mathematical models of key components 2. Validate models by comparing to COTS components 3. Build a virtual system from the models 4. Test virtual system for size, weight and efficiency

48 Physics-Based Analysis Reveals Principles

49 Overall efficiency (%) For Small Gaps, Cylinder Better Without Piston Seal Bore size 10 µ gap, 1450 psi Xia & Durfee, 52 nd Nat l Conf on Fluid Power, 2011

50 Comparing Electric to Hydraulic Using the Component Models

51 System Analysis Determines Which is Lighter POWER SUPPLY TRANSMISSION LINE ACTUATOR Electric POWER SUPPLY & CONTROL WIRE ELECTRIC MOTOR BALL SCREW Hydraulic POWER SUPPLY & CONTROL CONDUIT CYLINDER

52 System Weight (g) Fluid Power Lighter at High Pressures Without power supply and control Accounts for all component efficiencies Electric Fluid Power Power Supply and Control Power Supply and Control Wire Conduit Electric Motor Ball Screw Cylinder Electric 100 psi Hydraulic 500 psi Hydraulic 1000 psi Hydraulic Xia & Durfee, ASME J Mech Des, in review, ,000 Output Power (W)

53 Early Hydraulic AFO Prototype

54 500 psi, 3.4 kg, toe lift,

55 2,000 psi, 90 Nm, 100 deg/s

56 EEC R21HD