LVAD System Review System Overview Smiha Sayal System

LVAD System Review

System Overview Smiha 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 Process All team members

Other LVAD Technologies Cor. Aide (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.

P 10021’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 Generation See Handout

Concept Generation Highlights Bes Option 1 t O • Smallest internal volume • Feasible within timeline • Easiest to maintain • Minimum 20 wires ptio n Option 2 Option 3 • 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 153 249 200

Enclosure Design Nicole 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 See Handout Concept Generation- Material and Manufacturing Processes Rapid Prototyping (ABS Plastic) Stereolithography Injection Molded Machine Metal or Polymer Selection Criteria Weight Rating Notes Score Cost 9 4 36 1 9 1 $30 k for mold 9 2 18 Feasibility within timeline 10 5 50 4 long lead time 40 1 10 3 30 Strength 6 4 37 MPa 24 5 58 MPa 30 5 35 -70 MPa 30 5 ~580 MPa 30 Material Interaction with water 4 2 8 4 resin based 16 5 20 4 16 Ease of Manufacturing 3 5 15 3 9 0 0 20 wires 0 10 wires 0 3 wires 0 Net Score 133 110 78 103 Rank 1 2 3 4 Continue? yes No no no weight 1 - low importance 10 - high importance rating 1 - does not meet cirteria 5 - meets cirteria

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 D 638 5, 300 psi 37 MPa Tensile Modulus ASTM D 638 330, 000 psi 2, 320 MPa Tensile Elongation ASTM D 638 3% 3% Heat Deflection ASTM D 648 204°F 96°C Glass Transition DMA (SSYS) 226°F 108°C Specific Gravity ASTM D 792 1. 04 Coefficient of Thermal Expansion ASTM E 831 4. 90 E-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 – – – • • Risk: Water can enter the external package and harm the electronics Preventative measures: • 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

Feasibility- Water Ingress Test

Feasibility- Robustness Testing � � Need: The device should survive a fall from the hip Specification: Drop Test � Goal � Show the housing will not fail Show electronics package will not fail, when subjected to multiple drop tests Risks � 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 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: ~25 W Actual heat dissipation: ~5 W 250 Tout Tin Q h Internal Temperature [°C] � � � 200 150 100 Tout= Room Tout = Body 50 Absolute Max Temperature 0 0 t, k 5 10 15 20 25 Heat Generation, Q [W] 30 35 40

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 (6 mm) � 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 2 K 326 CLL Straight-Through Proposed: Part # EEG 2 K 326 CLV 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 Design Zack Shivers

Overall System Architecture See Handout

Interface Electronics 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

Interface Electronics USB connection See Schematic Page 2 RX / TX LEDs FTDI USB-to-Serial converter Transient voltage protection

Microcontroller See Schematic Page 5 �Microcontroller requires little electronics design �MCU needs: Clean 3. 3 V supply voltage I/O connections Programming interface (JTAG or BSL) Oscillator (optional)

HESA Signal Conditioning Hall Effect + Hall Effect - + _ ADC Input Voltage Clamping + Reference Voltage See Schematic Page 6 LPF Antialiasing filter

HESA Signal Conditioning See Schematic Page 6 Buffer circuit used as voltage reference for ADC

HESA Signal Conditioning - Calcs �Worst case voltage swing = 4 V – 2. 5 V = 1. 5 V �Differential output = +3 V �Resolution 12 -bit ADC 3. 3 V / 2^12 = 3. 3 V / 4096 = 0. 806 m. V / bit �Full Swing Digital 3. 0 V / 3. 3 V * 4096 = 3723 bits

AWB H-Bridges See Schematic Page 7 & 8 �Using TI DRV 8412 Dual Full-Bridge PWM Motor Controller �Heat dissipation PCB considerations Package is able to take 5 W at 25 degrees C Worst case power calculation: ▪ Ptotal = VDD * Iq + 2( Icond^2 * RDS(on) ) = 12 V (10. 5 m. A + 16 m. A) + 2 * (1 A)^2 * 120 mΩ = 0. 558 W Worst case power calculation does not exceed case No heatsink required, use grounded pad for heatsink

Brushless Controller See Schematic Page 9 �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

Voltage Regulation �Require multiple voltage supplies +3. 3 V, +5 V, +12 V Typical input voltage from batteries ranges from 12 V – 15 V �Step-down voltage converters Efficiently (upwards of 90%) convert large voltage to smaller voltages Disadvantage: injection of switching noise into supply voltages

Voltage Regulation Switcher. Pro from TI

Voltage Regulation Switching supply regulates from 12 -15 V to 3. 75 V with added switching noise See Schematic Page 10 Linear regulator attenuates switching noise, leaving clean 3. 3 V output Linear Technology “AN 101: Minimizing Switching Regulator Residue in Linear Regulator Outputs”. July 2005.

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 Switcher. PRO 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 System Andrew Hoag and Zack Shivers

Control System �Requirements Selecting suitable embedded control system Designing port of control logic to embedded system architecture �Customer 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 8 x 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 ds. PIC Microcontroller ▪ Blocks for Simulink ▪ Small ▪ Inexpensive (<$10 a piece) TI MSP 430 ▪ Inexpensive (<$8 a piece) ▪ Small, low power � COTS Embedded National Instruments Embedded ▪ Uses Lab. VIEW ▪ Manufacturer of current test and data acquisition system in “Big Black Box” ▪ Large to very large ▪ Very expensive (>$2000)

Microcontroller Selection Be Microcontroller Setups ds. PIC MSP 430 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 st Op Score 24 50 32 24 24 154 1 Yes See Handout tio n Notes Similar Zack has more MSP 430 experience MSP 430 ADC is 3. 3 V, sensors are 5 V Similar

MSP 430 F 5438 A - Specs �Specifications Max Frequency: 25 MHz Operating voltage: 1. 8 V – 3. 3 V Package: 100 pin LQFP Flash Memory: 256 KB RAM: 16 KB 87 General I/O pins ADC: 12 -bit SAR 4 x USCI_A (UART/LIN/Ir. DA/SPI) 4 x USCI_B (I 2 C/SPI) Timers 1 x 16 -bit (5 CCR) 1 x 16 -bit (3 CCR) 1 x 16 -bit (7 CCR) Watchdog RTC

MSP 430 F 5438 A - ADC �Greater than 200 - ksps maximum conversion rate �Able to acquire all 4 HESA signals in one shot without CPU intervention

MSP 430 F 5438 A - 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 16 x 16 mm) ▪ Marginally larger than 80 pin 5 xx devices with much more I/O and other peripherals

MSP 430 F 5438 A - 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

MSP 430 F 5438 A – 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 Elements See 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 IP 67 -rated � LEDs Provide basic, robust indicators � Buzzer Loud, high importance warnings Audible button feedback (beep when pressed)

User Interface Examples See 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 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

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-178 B

Software Use Cases See Handout �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.

A/D Sampling 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.

PWM Output 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.

Design: Control Law 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.

Design: Flowcharts A/D Interrupt Service Routine Startup and Main Loop

Current State of Development �The current baseline is available on the team’s EDGE subversion repository: https: //edge. rit. edu/dav/P 11021/design/software �This includes 3 rd party packages (Gtest), environment setup, and makefiles.

Power Amplifiers Juan Jackson

Amplifier Selection 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

AMB Control Center PWM Control Signal �Closed loop system �Stabilized by negative feedback �Power amplifiers increase power of PWM signals Full Bridge Power Amplifiers Active Magnetic Bearing System DAC Front. X Rear. X Impeller Rear. Y Front. Y Hall Effect Sensors (Senses Position) Microcontroller Four Degrees of freedom, Front. X, Front. Y, Rear. X, Rear. Y, which pushes rotor

Amplifier Selection Bes t O Linear Amplifier Selection Criteria Weight ptio n PWM Amplifier Rating Cost Notes Score Rating Notes Score 5 3 15 5 25 Feasibility within timeline 10 5 50 Fits Customer Requests 10 2 20 5 50 6 4 24 149 Ease of Design Net Score Weight 1 -Low importance 10 -High importance Rating 1 -Does not meet criteria 5 -Meets criteria 109

Amplifier Selection See Handout Bes AMB Amplifier Selection TLE 6209 R LMD 1800 Specificatio Selection Criteria Weight n Rating 10 Continuous Current Output (A) 3 5 10 Switching Frequency (k. Hz) 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 Designer Choice Customer Choice 3 rd 1 st t O Score 50 50 20 50 Specification Rating 3 5 5 2000 5 150 5 up to 45 -40°C ~ 50 5 150°C Surface 16 5 mount 236 2 2 nd ptio n DRV 8412 Score Specification Rating 50 6 5 500 50 5 80 50 5 50 -40°C ~ 85°C 40 290 1 Score 50 50 5 40 290 1 1 st 3 rd

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: MSP 430 F 5438 Also consider: Stellaris 5000 /8000 Series C 2000 - Fixed Point / Piccolo, Delfino MSP 430 - F 2 xx /5 xx 25 MHz ADS 7953 - 1 ch, 12 bit ADC BQ 2000 T - Battery Charge Management SN 65 HVD 23 3 - 3. 3 V CAN Transceiver TPS 40305 - DC/DC Controllers DRV 8412 - PWM Power Driver TPS 54620 - Step. Down Regulators Texas Instruments Microcontroller for Motor Control Applications : Component recommendation "MCU 4 Analog. " Texas Instruments, n. d. Web. 4 Nov 2010. <http: //focus. ti. com/mcu/docs/mcuorphan. tsp? content. Id=73295&DCMP=MCU_other&HQS=Other+OT

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