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XIV Brazilian Automatic Control Conference
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The Streamliner Artificial Heart
Brad PadenUniversity of California, Santa Barbara
& LaunchPoint Technologies LLC
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Outline
LVAD’s for artificial heart assist Background Next generation devices Design & Prototypes
– Actuators– Sensor– Control
Commercialization
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Need for Mechanical Need for Mechanical Circulatory AssistCirculatory Assist
15,000,000 heart disease deaths/yr. 5-10% could be saved with
circulatory assist Several options:
– Transplant (limited supply)– Ventricular assist device– Total artificial heart (not needed in
general)
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Heart Transplants in the US
2500/yr
2000/yr
1500/yr
1000/yr
500/yr
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Left Ventricular Assist Devices (LVAD) are the Leading Alternative to Transplants
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Lumped-element model of thecardiovascular system
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1st Generation LVADs are in use and are
pulsatile
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1st Generation Devices
Increase 2-year survival from 8% to 23% in end-stage heart failure patients*
Issues remain:– Thrombus (clot) formation,– Mechanical reliability.– Energy efficiency.
*Rose et al, “Long-term use of a left ventricular assist device for end-stageheart failure,” The New England Journal of Medicine, Vol 345(20), 2001
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1st Generation (pulsatile)
2nd Generation (rotary)
3rd Generation (maglev)
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Background on 3rd GenerationLVADs
Extracorporeal Prototypes (Olsen and Bramm, 1981; Allaire, Maslen, and Olsen, 1995; Chen et al, 1998)
Implantable devices in animal trials (StreamLiner 1998, TCI/Sulzer 1999, Berlin Heart ?)
Human Trials (Berlin Heart AG, June 16th 2002)
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Utah/UVA Mag-Lev LVAD
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Cleveland Clinic/Mohawk LVADCleveland Clinic/Mohawk LVAD
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LVAD Design Objectives
Avoid mechanical shearing of the blood
6 Liters/min and 100 mmHg High reliability and efficiency
– … hence magnetic bearings low power ~10 g loading
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Shear-Induced Hemolysis:a design constraint
L.B. Leverett et al, “Red Blood Cell Damage by Shear Stress,” Biophysical Journal, Vol. 12, pp. 257-273, 1972.
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1st Streamliner Concept(HemoGlide 1)
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Conical Bearing Prototypea wonderful 8x8, 10-state nonlinear multivariable control
problem. Stabilized using static linear decouplers and and 5 SISO lead-lag controllers.
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•In a divergence-free electric field there are no stable equilibria for charged particles.
•Similarly for ideal permanent magnets in astatic magnetic field.
This is too complicated!Can we just use permanent magnets?
Earnshaw’s Theorem (1842)
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more formally…
Let )( xEqF
, 0 E
, 0 E
, 0x
be an equilibrium point for a charge in the
field F
.
Since 0 E
there exists a real potential such that E
. Hence the
Jacobian qofHessianxd
Fd
and is therefore real sym m etric.
Further, real sym m etric m atrices have real eigenvalues and orthogonal eigenvectors.
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Theorem (Earnshaw): Let 321 ,, be the eigenvalues of the stiffness
matix xd
Fd
.
Then .0321 In particular, not all eigenvalues are negative
(i.e. there is no stable equilibrium). Proof: (the sum of the principle stiffnesses is a scalar multiple of the field divergence)
.0
321
Eq
dz
dF
dy
dF
dx
dF
xd
FdTr
zyx
Design Corollary: We can’t use all permanent magnet levitation...
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HG3 concept
But we can eliminate all but one active axis...
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JA Holmes
Final Design
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Section View and Final Device
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Jarvik-7, Novacor LVAD, HG3b
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HG3b Animal Trial (July ‘98)first fully maglev pump sufficiently compact and energy
efficient for implantation
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34 Day Animal Trial(August 24, 1999)
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Design Approach: Computer Modeling and Optimization
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TOPOLOGY SELECTION
FINITE ELEMENT
MODEL
LUMPED PARAMETER
MODELS
RAPID PROTOTYPE
IMPLANTABLE PROTOTYPE
OPTIMIZATION
OPTIMIZATION
Design Procedure
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Topology Selection (via design grammar)
(FH,AO) Sp - PRB-DCBM-ATB-PRB-Sp
|| ||
sb - ib - sb
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Lumped-Element Modeling and Finite-Element Analysis
Motor & Thrust Actuator– Lumped reluctance analysis
w/FEA-derived Correction Factors
– Some FEA optimization PM Bearings
– closed form solution of maxwell’s equations
– FEAanalysis Rotor
– rigid body model
– linear fluid damping
Controller, Actuator, Sensor– finite-dimensional models
Pump– Meanline Analysis
– Empirical Formulae
– Computational fluid dynamics (CFD)
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PM Bearing Design
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T a k e g a p < < R a n d i g n o r e e n d - e f f e c t s - > u s e 2 D m o d e l .
./2cos, znMMn
nODz
/2cos, zmMMm
mIDz
T h e s c a l a r m a g n e t i c p o t e n t i a l a t a p o i n t ( x , y , z ) d u e t o
i n n e r r a c e i s i n t e g r a l o f d i p o l e p o t e n t i a l s
dVr
MzyxU
IDV
ID
3
04
1),,(
r
.
z
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UHHH Tzyx },,{H .
T h e p o t e n t i a l e n e r g y o f a v o l u m ewdV OD
i n t h e f i e l d o f p l a t e I D i s
O DO D V
ODzIDz
V
ODID dVMHdVE ,,MH
y
wE
warea
forcepressure
),(1
. z
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+ s o m e c a l c u l u s …
nm
nmzneeB gndnr
y
if 0
if /2cos14 0
/22/2
0
2
I n t e g r a t i n g a r o u n d t h e r i n g s w i t h m = n = 1 .
deeeBLR
F xgdr cos14
cos/2/22/2
0
20
./214 1
/22/2
0
20
xIee
LRB gdr
s u m m i n g o v e r t h e v a r i o u s w a v e l e n g t h s y i e l d s t h e f o r c e f o r m u l a .
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PM Bearing Model
)/2(114
2
),,(1
/2/2
12
0
2
xnIeen
B
LR
dgxF gndn
oddn
r
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Motor Design
ROTOR
STATOR
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Motor Parameterization
R5 = 13.31
R3 = 5.936
R4 = 9.58
Ls =14.66W1 = 3.73
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Motor Optimization
2
1
3N = 5000 RPM = 85%P = 4W
V = 16.1
46
57
N = 15000 RPMV = 11.0
N = 10000 RPMV = 12.4
= 95%V = 40.2
= 90% V = 20.3
P = 16WV = 20.8
P = 8WV = 18.2
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Motor redesign and re-optimization to reduce radial instability
peakcoil
radial
NIBmm
mmB
r
mBB
,062
260
20
9
2
cos
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Pump Design (CFD)(James Antaki & Greg Burgreen)
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Final impeller design
• 5 impeller blade refinements• 4 internal flow path refinements• 6 aft stator blade refinements• 18 month development effort
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Flow visualization of early design
44XIV Brazilian Automatic Control Conference
8000 RPM
Hydrodynamic performance
Efficiency
PR
ES
SU
RE
mm
-Hg
0.160.150.140.130.120.110.100.090.080.070.060.050.040.030.020.01
FLOW RATE (LPM)
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Control system design
•Linear actuator with optimized force/watt1/2
•Virtual Zero Power (VZP) axial control (1.5W coil power while pumping)
•Ultra low-noise eddy-current sensors
•Sensorless Motor Control
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LPF+VoltageSense Amp
-1
1 MHzOsc.
CurrentDriver
s-a s+b
(-90 deg)
V(x)
L(x)x
C
1/(2(L(x0)C) ½) = 1MHz
-90º 90º
offsetadjust
mixer
Sensor System
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Ka (Ms2 -Kb )-1 Ks
Kp+Kd s
Ki/s
impeller axialdisturbance force
-
PID Controller
Linear Motor~2 N/ root watt
Rotor Mass &Bearing Negative Stiffness
Eddy-CurrentSensor
Pos. Reference= 0
PID Controller Structure(for reference only)
coil current
force displacement
noise~1Å / root Hz
heat
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Ka (Ms2 -Kb )-1 Ks
Kp+Kd s
Ki/s
impeller axialdisturbance force
-
VZP Controller
Linear Motor~2 N/ root watt
Rotor Mass &Bearing Negative Stiffness
Eddy-CurrentSensor
current reference = 0
Virtual Zero Power (VZP) Controller Structure*
coil current
force displacement
noise~1Å / root Hz
lessheat
s(Kp+Kd s)
Ki Kp +(1-Kd Ki)sAnti-windup included
*J. Lyman, “Virtually zero powered magnetic suspension,” US Pat. 3,860,300, 1975.
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Axial Disturbance Force
4 Newtons
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19 August 1999Streamliner HG3C sn001pre-implant
What is next?
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Commercialization
Teamed with MedQuest Products Inc, Salt Lake City, Utah.– commercially competitive engineering, clinical, and
business team.– a large maglev patent portfolio and has acquired
the Streamliner patents
Moved to a centrifugal pump design to maximize efficiency
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Conclusions Control engineers have much to offer
– System optimization is at the center of the design process
– The language of mathematics, objectives and constraints is essential
– Clever control design makes low-power maglev possible (Lyman Patent 1975)
Physiologic control is next...– Responsive to condition of heart and body
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Streamliner Team
Mechatronics– Brad Paden, Control
engineering– Chung-Ming Li, Analog
Design– Tom Dragnes, Electrical– Dave Paden,
Mechanical– Randy Crowsen,
Mechanical– Lina Arbelia, bio-
coatings– Nelson Groom, mag-lev
Fluids/Biological– James Antaki,
Streamliner Director– Greg Burgreen, CFD– Jon Wu, exp. fluids– Marina Kameneva,
blood damage– Phil Litwak,
veterinary surgery– Bartley Griffith,
surgery
Funding– McGowan Foundation
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MedQuest Products Team Mechatronics
– Brad Paden, & Garrick McNey,control engineering
– Jed Ludlow, dynamics
– Chung-Ming Li, electronics
– Dirk Cooley, electronics
– Dave Paden, Mechanical
– Randy Crowsen, Mechanical
Fluids/Biological– James Antaki, LVAD
design– Jon Wu, exp. fluids– Gordon Jacobs,
experimental– Jim Long, surgery– Don Olsen,
veterinary surgery
Business– Pratap
Khanwilkar, CEO
– Tim Walker, Marketing
Funding– NIH– Venture Capital
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The End