Transcript Display

Smiha Sayal

Left Ventricular
Assist Device (LVAD)
 Mechanical device that
helps pump blood from
the heart to the rest of
the body.

Implanted in patients
with heart diseases
or poor heart
function.
All team members
CorAide (NASA)
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

“Black box” architecture used during
development
Large, not portable
Runs on AC power

Miniaturize the existing LVAD system to
achieve portability while retaining its safety
and reliability.
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Has both internal / external components
Equivalent to our “Option 2”
Unfinished implementation
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Microcontroller used in the last year’s project
did not work.
The wires and the system were not robust
enough to perform testing of the system.
Testing of levitation and rotation was not
performed.
Space in the internal enclosure could have
been optimized by better placement of
internal components.
The enclosure was not ergonomic and nor was
it the most physically biocompatible shape.
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System needs to work
Safe
Robust
Affordable
Easy to wear and use
Interactive with user
Controllable by skilled technician
Comparable performance
Compatible with existing pump
Control system all external
ADC internal only
Amplifiers + MCU internal
All electronics and battery internal
Amplifiers internal
See
Handout
Option 1
Option 2
Option 3
• Smallest internal volume
• Feasible within timeline
• Easiest to maintain
• Minimum 20 wires
• Relatively small internal volume
• Slightly higher risk of internal
failure
• Minimum 10 wires
• Large internal volume
• Difficult to design
• Electronics failure is fatal
• Minimum 3 wires
350
273
Option 4
Option 5
• Large internal volume
• Difficult to design
• Electronics failure is fatal
• Minimum 3 wires
• Moderate internal volume
• Difficult to design
• Electronics failure is fatal
• Minimum X wires
153
200
249
Nicole Varble and Jason Walzer
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Needs
 The external package should be lightweight/ robust/ water
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resistant
The devices should be competitive with current devices
The device should fit into a small pouch and be comfortable for
user and be comfortable for the user
The external package should resist minor splashing
The device should survive a fall from the hip
Risks
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Housing for the electronics is too heavy/large/uncomfortable
Water can enter the external package and harm the electronics
The housing fails before the electronic components in drop tests
The electronic components can not survive multiple drop tests
See
Handout
Concept Generation- Material and Manufacturing Processes
Manufacturing Processes
Rapid Prototyping (ABS
Plastic)
Selection Criteria
Weight
Rating
Notes
Score
Cost
9
4
36
Feasibility within timeline
10
5
50
Strength
6
4
37 MPa
24
Material Interaction with water
4
2
8
Ease of Manufacturing
3
5
15
0
20 wires
0
Net Score
133
Rank
1
Continue?
yes
weight
1- low importance
10- high importance
rating
1- does not meet cirteria
5- meets cirteria
Stereolithography
Rating
Notes
Score
1
9
4
long lead time 40
5
58 MPa
30
4
resin based
16
5
15
0
10 wires
0
110
2
No
Injection Molded
Rating
Notes
Score
1
$30k for mold 9
1
10
5
35-70 MPa
30
5
20
3
9
0
3 wires
0
78
3
no
Machine Metal or Polymer
Rating
Notes
Score
2
18
3
30
5
~580 MPa
30
4
16
3
9
0
3 wires
0
103
4
no
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Machinable
 Material can be drilled and tapped
•
(carefully)
Accepts CAD drawings
– Complex geometries can be created
•
easily
– Ideal for proposed ergonomic shape
Builds with support layer
– Models can be built with
working/moving hinges without having
to worry about pins
• Capable of building thin geometries
• ABSplus
– Industrial thermoplastic
• Lightweight - Specific gravity of 1.04
• Porous
– Does not address water resistant need
http://www.dimensionprinting.com/
Mechanical
Property
Test
Method
Imperial
Metric
Tensile Strength
ASTM D638
5,300 psi
37 MPa
Tensile Modulus
ASTM D638
330,000 psi
2,320 MPa
Tensile Elongation
ASTM D638
3%
3%
Heat Deflection
ASTM D648
204°F
96°C
Glass Transition
DMA (SSYS)
226°F
108°C
Specific Gravity
ASTM D792
1.04
1.04
Coefficient of
Thermal Expansion
ASTM E831
4.90E-5 in/in/F
•
Important Notes
• Relatively high tensile strength
• Glass Transition well above body temperature
• Specific Gravity indicates lightweight material
•
•
Need: The external package should resist
minor splashing
Specification: Water Ingress Tests
–
–
–
•
•
Risk: Water can enter the external
package and harm the electronics
Preventative measures:
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Once model is constructed, (user interface,
connectors sealed, lid in place) exclude internal
electronics and perform test
Monitor flow rate (length of time and volume) of
water
Asses the quality to which water is prevented from
entering case by examining water soluble paper
Spray on Rubber Coating or adhesive
O-rings around each screw well and around the lid
Loctite at connectors
Preliminary Tests without protective
coating show no traceable water ingress
Loctite
Spray on Rubberized Coating
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Need: The device should survive a fall from the hip
Specification: Drop Test
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Goal
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Show the housing will not fail
Show electronics package will not fail, when subjected to
multiple drop tests
Risks
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Drop external housing 3 times from 1.5 m, device should
remain fully intact
Specify and build internal electrical components
Identify the “most vulnerable” electrical component(s)
which may be susceptible to breaking upon a drop
Mimic those components using comparable (but
inexpensive and replaceable) electrical components, solder
on point to point soldering board
The housing fails before the electronic components in drop
tests (proved unlikely with prototype enclosure)
The electronic components can not survive multiple drop
tests
Preventative Measures
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Eliminate snap hinges from housing (tested and failed)
Test the housing first
Design a compact electronics package
130°C is absolute maximum for chip junction temperature in order to function properly
Goal: comfort for the user
Assumed steady state, heat only dissipated through 3 external surfaces
Maximum heat dissipation: ~25W
Actual heat dissipation: ~5W
250
Tout
Tin
Q
h
Internal Temperature [°C]
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200
150
100
Tout= Room
Tout = Body
50
Absolute Max Temperature
0
0
5
10
15
20
25
Heat Generation, Q [W]
t, k
30
35
40
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Survived drop test
Water resistant
Plastic is machinable
 Drilled, tapped, milled
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Helicoils should be used to tap
holes
 Constant opening and
screwing and unscrewing of lid
will result in stripped threads
Approximate wall thickness
(6mm)
 Distance between center of
holes and wall needs to be
increased
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 Some cracking occurred
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Latches are not feasible
LED Backlit display with waterproof bezel and o-ring
G/R/Y LEDs with O-ring and
waterproof bezel
Waterproof buttons with O-ring
Current Model: Part # EGG 2K 326 CLL
Straight-Through
Proposed: Part # EEG 2K 326 CLV
Right-Angle,
PCB mount
See Handout
on IP Ratings
UI Item
IP Rating
Display
IP 67
Buttons
IP 67
LEDs
IP 67
USB
IP 68
Connector
IP 68
Zack Shivers
See Handout
See Schematic
Page 2

Interfaces:
 26-pin pump connector
▪ Will be directly compatible with old connector!
 JTAG (for direct programming)
 FTDI USB-to-serial converter
 Reset pushbutton
See Schematic
Page 2
RX / TX LEDs
USB connection
FTDI USB-to-Serial
converter
Transient voltage
protection
See Schematic
Page 5
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
Microcontroller requires little electronics
design
MCU needs:
 Clean 3.3V supply voltage
 I/O connections
 Programming interface (JTAG or BSL)
 Oscillator (optional)
See Schematic
Page 6
Hall Effect +
Hall Effect -
+
_
ADC Input
Voltage
Clamping
+
Reference Voltage
LPF Antialiasing filter
See Schematic
Page 6
Buffer circuit used as
voltage reference
for ADC
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Worst case voltage swing = 4V – 2.5V = 1.5V
Differential output = +3V
Resolution
 12-bit ADC
 3.3V / 2^12 = 3.3V / 4096 = 0.806 mV / bit
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Full Swing Digital
 3.0V / 3.3 V * 4096 = 3723 bits
See Schematic
Page 7 & 8
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Using TI DRV8412 Dual Full-Bridge PWM Motor
Controller
Heat dissipation PCB considerations
 Package is able to take 5W at 25 degrees C
 Worst case power calculation:
▪ Ptotal = VDD * Iq + 2( Icond^2 * RDS(on) )
= 12V (10.5 mA + 16 mA) + 2 * (1A)^2 * 120mΩ
= 0.558W
 Worst case power calculation does not exceed case
 No heatsink required, use grounded pad for heatsink
See Schematic
Page 9
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Per customer request, we will continue to use
the COTS PHX-35 controller from Castle
Creations
Added connectors to board to interface with
this part
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Require multiple voltage supplies
 +3.3V, +5V, +12V
 Typical input voltage from batteries ranges from
12V – 15V
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Step-down voltage converters
 Efficiently (upwards of 90%) convert large voltage
to smaller voltages
 Disadvantage: injection of switching noise into
supply voltages
SwitcherPro from TI
See Schematic
Page 10
Switching supply regulates
from 12-15V to 3.75V with
added switching noise
Linear regulator attenuates
switching noise, leaving
clean 3.3V output
Linear Technology “AN101: Minimizing Switching Regulator Residue
in Linear Regulator Outputs”. July 2005.

Why will the electronics work?
 Difference amplifiers with filter worked for last
team
 Brushless controller is COTS
 MCU crystal and JTAG circuitry taken directly from
TI development boards
 Professionally created tool SwitcherPRO used for
design of voltage regulation circuits
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How will we verify electronics meet spec?
 Header breakouts for all signals allows for debug and
verify at each subsystem
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Unit tests
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AWB amplifier test
HESA signal acquisition
PHX-35 test with MCU input
Power regulation test
LED + Button test
Graphic LCD test
Andrew Hoag and Zack Shivers
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Requirements
 Selecting suitable embedded control system
 Designing port of control logic to embedded
system architecture
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Customer Needs
 Device is compatible with current LVAD
 Device is portable/small
 Allows debug access
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Impeller must be levitating or “floating”
Electromagnets control force exerted on impeller
Keeps impeller stabilized in the center
Position error measured by Hall Effect sensors
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Algorithm complexity influences
microcontroller choice
 Electronics choices affect volume / weight
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Proportional – Integral – Derivative (PID)
 Very common, low complexity control scheme
http://en.wikipedia.org/wiki/PID_controller
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Requirements:
 Can handle PID calculations
 Has at least 8x 12-bit ADC for sensors at 5000
samples/sec
 Multiple PWM outputs to motor controller(s)
 Same control logic as current LVAD system
 Reprogrammable
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Custom Embedded
 dsPIC Microcontroller
▪ Blocks for Simulink
▪ Small
▪ Inexpensive (<$10 a piece)
 TI MSP430
▪ Inexpensive (<$8 a piece)
▪ Small, low power
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COTS Embedded
 National Instruments
Embedded
▪ Uses LabVIEW
▪ Manufacturer of current test
and data acquisition system in
“Big Black Box”
▪ Large to very large
▪ Very expensive (>$2000)
See Handout
Microcontroller Setups
dsPIC
MSP430
Selection Criteria
Weight
6
10
8
6
6
Rating
4
2
5
4
4
Score
24
20
40
24
24
132
2
No
Cost
Feasibility within timeline
A/D
Ease of design
Ease of manufacturing
Net Score
Rank
Continue?
Weight Scale 1 - Low importance
10 - High importance
Rating Scale 1 - Does not meet cirteria
5 - Meets cirteria
Rating
4
5
4
4
4
Score
24
50
32
24
24
154
1
Yes
Notes
Similar
Zack has more MSP430 experience
MSP430 ADC is 3.3V, sensors are 5V
Similar
Similar

Specifications
 Max Frequency: 25MHz
 Operating voltage:
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1.8V – 3.3V
Package: 100 pin LQFP
Flash Memory: 256 KB
RAM: 16 KB
87 General I/O pins
ADC: 12-bit SAR
 4x USCI_A
(UART/LIN/IrDA/SPI)
 4x USCI_B (I2C/SPI)
 Timers
 1x 16-bit (5CCR)
 1x 16-bit (3CCR)
 1x 16-bit (7CCR)
 Watchdog
 RTC
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Greater than 200ksps maximum
conversion rate
Able to acquire all 4
HESA signals in one
shot without CPU
intervention
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How does this chip meet the specifications?
 Fast
▪ Dedicated peripherals like timers and UART reduce CPU usage
▪ Able to execute full PID algorithm with minimal CPU usage
 Spacious
▪ Large RAM and program space
▪ Able to execute programs much larger this application
 Able to generate 12 PWM signals (only need 5)
 Physical Size
▪ Small portion of expected PCB layout (only 16x16 mm)
▪ Marginally larger than 80 pin 5xx devices with much more I/O and
other peripherals
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Confidence in ability to program and
interface with hardware
 Was able to program an actual chip with breakout
board
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Standard high-end TI MCU
 Hundreds of code examples available for this
specific chip

Previous experience
 Over 3 months of experience at TI with this
specific chip

Optional / Cool Future Features
 Ability to program using bootstrap loader (BSL)
over USB instead of JTAG
 Data dump to USB
▪ Temperature, current, RPM
 PONG (not really…)
Graphic
LCD
Buttons
LEDs
Buzzer
See Handout

Why use an LCD?
 Display much more information
 Interactivity
 Allows interface modes for technician and user

Buttons
 Up, Down, and Menu for interaction
 IP67-rated

LEDs
 Provide basic, robust indicators

Buzzer
 Loud, high importance warnings
 Audible button feedback (beep when pressed)
See Handout

How do we know UI will work / meet specs?
 Portable, proven example code online for LCD
display
 Buttons / LED interfacing is standard and very
simple
 If graphic menu system is too complex, can fall
back to simpler modes
▪ LCD text only
▪ LED and button interaction only
Andrew Hoag
See Handout

Described in Software Design Plan/Software
Design Document
 Coding Standards – ANSI C, File headers,
comments
 Code Reviews – EE/CE team will review all
changes
 Unit and Integration testing

Software unit and integration tests using
Gtest (Google Testing Framework) – an open
source test framework for C/C++
 Results/artifacts for coverage, pass and failure.
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Code Coverage – the degree to which source
code has been covered in software tests. It is
required in safety-critical systems.
FDA has released guidelines and
recommendations for code coverage.
DO-178B
See Handout
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The software shall sample HESA values at
fs=5000, input to the control loop, and update
the AMB PWM outputs.
The software shall report battery level, faults,
and status to the user.
The software shall respond to user input to
adjust pump motor speed.
The software shall provide a verbose
technician/engineering debug output.
The software shall be robust and reliable for a
safety-critical system.
See Handout


Each of the HESA analog channels is sampled
at 5 kilo-samples/second.
The software shall make use of the ADC
timers and interrupts provided by the
microcontroller architecture to control the
sampling.
See Handout


Pulse-width Modulation is a digital signal that
is used to simulate an analog output by
varying high and low signals at intervals
proportional to the value.
The AMB is controlled using 4 PWM signals.
The pump motor is controlled using a single
PWM output.
See Handout

PID: common feedback control loop that is
currently used in the LVAD control system.
 The output signal is a function of the error, the
error’s history, and the error’s rate of change.
A/D Interrupt Service Routine
Startup and Main Loop

The current baseline is available on the
team’s EDGE subversion repository:
https://edge.rit.edu/dav/P11021/design/software

This includes 3rd party packages (Gtest),
environment setup, and makefiles.
Juan Jackson
Linear
PWM
• Higher power to load
• Low efficiency
•
•
•
•
High frequency switching
Capable of higher power than the linear amplifier
Better performance at higher frequencies
High efficiency
PWM Control Signal
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Closed loop
system
Stabilized by
negative
feedback
Power amplifiers
increase power of
PWM signals
Full Bridge
Power Amplifiers
Active Magnetic
Bearing System
DAC
RearX
FrontX
Impeller
RearY
FrontY
Hall Effect Sensors
(Senses Position)
Microcontroller
Four Degrees of freedom,
FrontX, FrontY, RearX, RearY,
which pushes rotor
Linear Amplifier
Selection Criteria
Weight
Cost
Rating
PWM Amplifier
Notes
Score
Rating
Notes
Score
5
3
15
5
25
Feasibility within
timeline
10
5
50
5
50
Fits Customer Requests
10
2
20
5
50
6
4
24
4
24
Ease of Design
Net Score
Weight
109
1-Low importance
10-High
importance
Rating
1-Does not meet
criteria
5-Meets criteria
149
See Handout
LMD1800
Specificatio
Selection Criteria
Weight
n
Rating
10
Continuous Current Output (A)
3
5
10
Switching Frequency (kHz)
100
5
10
Rdson (mΩ)
330
2
10 12 to 55
Operating Supply Voltage (V)
5
-40°C ~
10
Temperature (°C)
125°C
5
Through
8
2
Package Type
hole
Net Score
Rank
AMB Amplifier Selection
TLE6209R
Score
50
50
20
50
50
16
236
2
Specification Rating
3
5
5
2000
5
150
5
up to 45
-40°C ~
5
150°C
Surface
5
mount
DRV8412
Score Specification
Rating
50
6
5
50
5
500
50
5
80
50
5
50
-40°C ~ 85°C
40
290
1
Designer Choice
3rd
2nd
1st
Customer Choice
1st
2nd
3rd
Score
50
50
50
50
5
50
5
40
290
1
Texas Instrument Application
Diagram for Full Bridge
Mode Operation
Motor Control - DC
Brushless
BLDC motors are more efficient,
run faster and quieter, and
require electronics to control the
rotating field. BLDC motors are
also cheaper to manufacture and
easy to maintain
Recommended:MSP430F5438
Also consider:
Stellaris 5000 /8000 Series
C2000 - Fixed Point / Piccolo,
Delfino
MSP430 - F2xx /5xx 25MHz
ADS7953 1ch, 12 bit
ADC
BQ2000T Battery Charge
Management
SN65HVD23
3 - 3.3V CAN
Transceiver
TPS40305 DC/DC
Controllers
DRV8412 PWM Power
Driver
TPS54620 - StepDown Regulators
Texas Instruments Microcontroller for Motor Control Applications :
Component recommendation
"MCU4Analog." Texas Instruments. Texas Instruments, n.d. Web. 4 Nov 2010.
<http://focus.ti.com/mcu/docs/mcuorphan.tsp?contentId=73295&DCMP=MCU_other&HQS=Other+OT
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