LVAD System Review

System OverviewSmiha Sayal

System Overview

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.

Engineering ProcessAll team members

Other LVAD Technologies

CorAide (NASA)

Other LVAD Technologies

Original System

“Black box” architecture used during development

Large, not portable Runs on AC power

System Goal

Miniaturize the existing LVAD system to achieve portability while retaining its safety and reliability.

P10021’s System

Has both internal / external components Equivalent to our “Option 2” Unfinished implementation

Previous Team Shortcomings 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.

Customer Needs

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

Concepts: Option 1

Control system all external

Concepts: Option 2

ADC internal only

Concepts: Option 3

Amplifiers + MCU internal

Concepts: Option 4

All electronics and battery internal

Concepts: Option 5

Amplifiers internal

Concept GenerationSee

Handout

Concept Generation Highlights

Option 1• Smallest internal volume• Feasible within timeline• Easiest to maintain• Minimum 20 wires

Option 2• Relatively small internal volume

• Slightly higher risk of internal failure

• Minimum 10 wires

Option 3• Large internal volume• Difficult to design• Electronics failure is fatal• Minimum 3 wires

Option 4• Large internal volume• Difficult to design• Electronics failure is fatal• Minimum 3 wires

Option 5• Moderate internal volume• Difficult to design• Electronics failure is fatal• Minimum X wires

Best Option

350

273

200

153

249

Enclosure DesignNicole Varble and Jason Walzer

External Enclosure

Needs The external package should be lightweight/ robust/ water

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 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

Concept Generation- Materials/Manufacturing Process

Concept Generation- Material and Manufacturing Processes

Manufacturing Processes

Rapid Prototyping (ABS

Plastic) Stereolithography Injection Molded Machine Metal or PolymerSelection Criteria Weight Rating Notes Score Rating Notes Score Rating Notes Score Rating Notes ScoreCost 9 4 36 1 9 1 $30k for mold 9 2 18Feasibility within timeline 10 5 50 4 long lead time 40 1 10 3 30Strength 6 4 37 MPa 24 5 58 MPa 30 5 35-70 MPa 30 5 ~580 MPa 30Material Interaction with water 4 2 8 4 resin based 16 5 20 4 16Ease of Manufacturing 3 5 15 5 15 3 9 3 9 0 0 0 0 20 wires 0 10 wires 0 3 wires 0 3 wires 0Net Score 133 110 78 103Rank 1 2 3 4

Continue? yes No no noweight 1- low importance

10- high importancerating 1- does not meet cirteria

5- meets cirteria

SeeHando

ut

Rapid Prototyping

• 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/

ABS Plastic

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

Feasibility- Water Ingress Test

• Need: The external package should resist minor splashing

• Specification: Water Ingress Tests– 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

• Risk: Water can enter the external package and harm the electronics

• Preventative measures: 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

Spray on Rubberized CoatingLoctite

Feasibility- Water Ingress Test

Feasibility- Robustness Testing

Need: The device should survive a fall from the hip Specification: Drop Test

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

Goal Show the housing will not fail Show electronics package will not fail, when subjected

to multiple drop tests Risks

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 Eliminate snap hinges from housing (tested and failed) Test the housing first Design a compact electronics package

Feasibility- Heat Dissipation of Internal Components

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

t, k

Q

Tin

Tout

h

0 5 10 15 20 25 30 35 400

50

100

150

200

250

Tout= RoomTout = BodyAbsolute Max Tempera-ture

Heat Generation, Q [W]

Inte

rnal Tem

pera

ture

[°C

]

Prototype Enclosure

Survived drop test Water resistant Plastic is machinable

Drilled, tapped, milled 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 Some cracking occurred

Latches are not feasible

User Interface - Components

LED Backlit display with waterproof bezel and o-ring

G/R/Y LEDs with O-ring and waterproof bezel

Waterproof buttons with O-ring

User Interface - Connectors

Current Model: Part # EGG 2K 326 CLL

Proposed: Part # EEG 2K 326 CLV

Straight-Through

Right-Angle, PCB mount

User Interface- IP Codes

UI Item IP Rating

Display IP 67

Buttons IP 67

LEDs IP 67

USB IP 68

Connector IP 68

See Handout

on IP Ratings

Enclosure Design

Enclosure Design

Enclosure Design

Electronics DesignZack Shivers

Overall System Architecture

See Handout

Interface Electronics

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

Interface ElectronicsSee

Schematic Page 2

Transient voltage protection

USB connection

FTDI USB-to-Serial converter

RX / TX LEDs

Microcontroller

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 5

HESA Signal Conditioning

+

_

LPF Anti-aliasing filter

Hall Effect +Hall Effect -

ADC InputVoltage

Clamping+

Reference Voltage

See Schematic

Page 6

HESA Signal ConditioningSee

Schematic Page 6

Buffer circuit used as voltage

reference for ADC

HESA Signal Conditioning - Calcs

Worst case voltage swing = 4V – 2.5V = 1.5V

Differential output = +3VResolution

12-bit ADC 3.3V / 2^12 = 3.3V / 4096 = 0.806

mV / bitFull Swing Digital

3.0V / 3.3 V * 4096 = 3723 bits

AWB H-Bridges

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 7 & 8

Brushless Controller

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

See Schematic

Page 9

Voltage Regulation

Require multiple voltage supplies +3.3V, +5V, +12V Typical input voltage from batteries

ranges from 12V – 15V Step-down voltage converters

Efficiently (upwards of 90%) convert large voltage to smaller voltages

Disadvantage: injection of switching noise into supply voltages

Voltage Regulation

SwitcherPro from TI

Linear Technology “AN101: Minimizing Switching Regulator Residue in Linear Regulator Outputs”. July 2005.

Voltage Regulation

Switching supply regulates from 12-15V to 3.75V with added switching noise

Linear regulator attenuates switching noise, leaving clean 3.3V output

See Schematic Page 10

Feasibility

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

Electronics Testing

How will we verify electronics meet spec? Header breakouts for all signals allows for

debug and verify at each subsystem Unit tests

AWB amplifier test HESA signal acquisition PHX-35 test with MCU input Power regulation test LED + Button test Graphic LCD test

Embedded Control SystemAndrew Hoag and Zack Shivers

Control System

Requirements Selecting suitable embedded control

system Designing port of control logic to

embedded system architectureCustomer Needs

Device is compatible with current LVAD Device is portable/small Allows debug access

Impeller Levitation

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

Levitation Algorithm

Algorithm complexity influences microcontroller choice Electronics choices affect volume / weight

Proportional – Integral – Derivative (PID) Very common, low complexity control scheme

http://en.wikipedia.org/wiki/PID_controller

Embedded System Selection

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

Embedded System Selection

Custom Embedded dsPIC

Microcontroller Blocks for Simulink Small Inexpensive (<$10 a

piece) TI MSP430 Inexpensive (<$8 a

piece) Small, low power

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)

Microcontroller Selection

Microcontroller Setups

Selection Criteria Weight

dsPIC MSP430

NotesRating Score Rating ScoreCost 6 4 24 4 24 SimilarFeasibility within timeline 10 2 20 5 50 Zack has more MSP430 experienceA/D 8 5 40 4 32 MSP430 ADC is 3.3V, sensors are 5VEase of design 6 4 24 4 24 SimilarEase of manufacturing 6 4 24 4 24 SimilarNet Score 132 154 Rank 2 1 Continue? No Yes

Weight Scale 1 - Low importance10 - High importance

Rating Scale 1 - Does not meet cirteria 5 - Meets cirteria

Best Option

See Handout

MSP430F5438A - Specs

Specifications Max Frequency: 25MHz Operating voltage:

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

MSP430F5438A - ADC

Greater than 200-ksps maximum conversion rate

Able to acquire all 4 HESA signals in one shot without CPU intervention

MSP430F5438A - Feasibility 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

MSP430F5438A - Feasibility Confidence in ability to program and

interface with hardware Was able to program an actual chip with

breakout board 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

MSP430F5438A – Cool Features

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…)

User Interface Elements

Graphic LCD Buttons

LEDs Buzzer

User Interface ElementsSee Handout

User Interface

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)

User Interface ExamplesSee Handout

UI Feasibility

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

Software Andrew Hoag

Quality

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

See Handout

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.

Testing

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

Software Use Cases

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

A/D Sampling

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

PWM Output

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

Design: Control Law

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.

See Handout

Design: Flowcharts

Startup and Main Loop

A/D Interrupt Service Routine

Current State of Development

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.

Power AmplifiersJuan Jackson

Amplifier Selection

•Higher power to load

•Low efficiency

Linear

•High frequency switching

•Capable of higher power than the linear amplifier

•Better performance at higher frequencies

•High efficiency

PWM

AMB Control Center

Four Degrees of freedom, FrontX, FrontY, RearX, RearY, which pushes rotor

DAC

Microcontroller

PWM Control Signal

Full BridgePower Amplifiers

Active Magnetic Bearing System

ImpellerFrontX

FrontY

RearX

RearY

Hall Effect Sensors(Senses Position)

Closed loop system

Stabilized by negative feedback

Power amplifiers increase power of PWM signals

Amplifier Selection

Linear Amplifier

PWM Amplifier

Selection Criteria Weight Rating Notes Score Rating Notes Score

Cost 5 3 15 5 25

Feasibility within timeline 10 5 50 5 50

Fits Customer Requests 10 2 20 5 50

Ease of Design 6 4 24 4 24

Net Score 109 149

Weight 1-Low importance

10-High importance

Rating1-Does not meet criteria

5-Meets criteria

Best Option

Amplifier Selection

AMB Amplifier Selection LMD1800 TLE6209R DRV8412

Selection Criteria WeightSpecificatio

n Rating Score Specification Rating Score Specification Rating ScoreContinuous Current Output (A) 10 3 5 50 3 5 50 6 5 50Switching Frequency (kHz) 10 100 5 50 2000 5 50 500 5 50Rdson (mΩ) 10 330 2 20 150 5 50 80 5 50Operating Supply Voltage (V) 10 12 to 55 5 50 up to 45 5 50 5 50

Temperature (°C) 10-40°C ~ 125°C 5 50

-40°C ~ 150°C 5 50 -40°C ~ 85°C 5 50

Package Type 8Through hole 2 16

Surface mount 5 40 5 40

Net Score 236 290 290Rank 2 1 1

Designer Choice 3rd 2nd 1st

Customer Choice 1st 2nd 3rd

See Handout

Best Option

Amplifier Proof of Concept

Texas Instrument Application Diagram for Full Bridge

Mode Operation

Amplifier Proof of Concept

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:MSP430F5438Also consider:Stellaris 5000 /8000 SeriesC2000 - Fixed Point / Piccolo, DelfinoMSP430 - F2xx /5xx 25MHz

ADS7953 - 1ch, 12 bit ADC

BQ2000T - Battery Charge Management

SN65HVD233 - 3.3V CAN Transceiver

TPS40305 - DC/DC Controllers

DRV8412 - PWM Power Driver

TPS54620 - Step-Down 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

Questions / CommentsHelp us improve our design!