P11021 System ReviewMiniaturization of RIT’s LVAD Electronics Package

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.

Original System“Black box” architecture used during

developmentLarge, not portableRuns on AC power

System Goal

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

Concepts

Control system all external

Enclosure DesignNicole Varble and Jason Walzer

External Enclosure Needs

Lightweight Robust Competitive with current devices Easily portable and comfortable for user Resist splashing 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

Enclosure Features Dimensions: 180 x 82 x 103 mm

Volume ~ 1,500 cm3

Current Controller ~ 12,700 cm3

Heart Mate II ~ 820 cm3

Percentage Reduction: 88 %

Weight: ~560 g Heart Mate II ~ 602 g

Other features: Helicoils to reinforce threads in ABS plastic Plasti- dip coating Ergonomic curve against body Belt-loop for portability Custom made 0-ring

Enclosure Testing Drop Test:

Enclosure dropped 1.5 m above ground level and was tested for damage

Results: No visible cracks or fissures were observed.

Water Ingress Test: Enclosure was sprayed on with a rubberized coating

and was held under a faucet with a flow rate of about 2 gpm for about 1 min

Results: Not submersible but can endure running water

Heat Dissipation: Max temperature inside the box was analytically

calculated to be 79°C Under the max critical operating temperature of

electronics

Short comings / Recommendations Drop Test:

Use enclosure with similar components to current prototype

High risk of permanent damage

Heat Analysis: Many broad assumptions (often over compensating) Temperature calculated was close to the critical

working temperature of electronics (~85°C ) In-depth experimental analysis could have been

conducted

Electronics DesignZack Shivers and Juan Jackson

Electronics Overview

HESA Signal Conditioning

Before Scaling

29% ADC Range

After Scaling98% of

ADC Range

1.6V 2.58V

3.3V0V 0V

0.01V

3.0V

2.94V

HESA Signal Conditioning

Hall effect sensors are natively 5V Divide to 3.3V levels Use 3.0V ref for ADC RC anti-aliasing filter

Effective transformation Voltage divider Buffer Subtract 1.6V and

gain up by factor of 3

Impeller Speed Controller3-phase motor controller

Used to control impellerOff-the-shelf component

Suggested to us by the customer as tested and reliable controller

Simplified our design Interface

Standard RC PWM signal, low resolution

Active Magnetic Bearing

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

Active Magnetic Bearings

P10021’s System:

8280 mm3

Our System:

282 mm3

Only 3.40% of previous prototype!

DRV8412

LMD18200

On-Board Power Supplies

Need to overall system at 15V 3.3V and 5V needed at relatively high power

Generated with high-efficiency switching power supplies

15V used directly for AMB system Various references for HESA and DAC

15V

3.3V 5.0V 12V 5.0V Ref

3.0V Ref

1.60V Ref

On-Board Power Supplies

~85% efficient for loads > 0.35A

Printed Circuit Board

Printed Circuit Board

Printed Circuit Board

Printed Circuit Board

HESA

UI

AMB

uC Power

PCB Results

Passes all hardware tests Microcontroller 3.3V, 5V, and 12V power supplies H-bridges HESA signal conditioning

No cut/reworked traces

Embedded Control SystemAndrew Hoag

MSP430F5438A

Texas Instruments MSP430 Microcontroller

MSP430F5438A Specifications

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 

Our Configuration

MSP430 Operating at 20MHz Using less than 16kB memory HESA values sampled 5000 times per

second using Analog-to-Digital converter

Software

Software Controller

software written in C using Texas Instruments Code Composer Studio.

Technician/debug client software written in Java.

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 AMBs PWM signals are generated using four 20kHz PWM signals generated by Timer A0.

The 3-phase motor PWM signal is generated using a 50Hz PWM signal generated by Timer B.

Motor PWM Test Results

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.

Debug Data

Debug information is transmitted to a PC at 115200 baud using serial RS-232 over USB.

Centering test results:

User Interface Elements

Graphic LCD Buttons

LEDs Buzzer

User Interface Elements

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)

System Analysis

Customer Needs

System needs to workSafeRobustAffordableEasy to wear and use Interactive with userControllable by skilled technicianComparable performanceCompatible with existing pump

Customer SpecificationsEngr.

Spec. # Source Specification (description) Unit of Measure

Marginal Value

Ideal Value Actual Comments/Status

ES101-1 CN101 Weight of device lbs 6 4 1.22 MetES101-2 CN101 Volume of device cu in 75 56 91.5 Not Met

ES102-1 CN103Device running time (full charge-needing recharge) hours 6 12 Not Met

ES103-1 CN103 Device recharge time hours < 2 1 Not MetES105-1 CN105 AC mains power binary 0 1 1 Met

ES203-1 CN203Device running time between swapping batteries hours 0.25 >0.5 Not Met

ES302-1 CN302 Battery information is indicated binary 0 1 1 MetES303-1 CN303 User control of pump rotation speed binary 1 1 1 MetES401-1 CN401 Hardware signal debug port binary 0 1 1 MetES402-1 CN402 Device is reprogrammable binary 1 1 1 MetES403-1 CN403 Manual speed control binary 1 1 1 MetES500-1 CN500 Device price dollars <4000 2000 1400 MetES601-1 CN601 Device lifetime expectancy years 0.5 20 Not Met ES701-1 CN701 Battery life vs. competitor life % -50 100 Not Met ES702-1 CN702 Device weight vs. competitor weight lbs  1.33 > 1.33 1.22 Met

ES-802-1 CN802 Device heat dissipationmW/

cm^2 40 <40 11.4 Met

Schedule

Initial Plan: Final Assembly by Week 7 followed by testing.

Actual Plan: The plan was delayed by 2 weeks. Assembly was done in week 9 followed by testing in week 10.

Current Status: Continuing Testing. System Demo to be done by mid Week 11.

Budget

Initial Budget: The design was estimated to cost $ 1,000.

Current Status: Currently ~$1,400 has been spent.

Questions / Comments