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LVAD System Review

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.

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LVAD System Review

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  1. LVAD System Review

  2. System Overview SmihaSayal

  3. 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.

  4. Engineering Process All team members

  5. Other LVAD Technologies CorAide (NASA)

  6. Other LVAD Technologies

  7. Original System • “Black box” architecture used during development • Large, not portable • Runs on AC power

  8. System Goal • Miniaturize the existing LVAD system to achieve portability while retaining its safety and reliability.

  9. P10021’s System • Has both internal / external components • Equivalent to our “Option 2” • Unfinished implementation

  10. 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.

  11. 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

  12. Concepts: Option 1 Control system all external

  13. Concepts: Option 2 ADC internal only

  14. Concepts: Option 3 Amplifiers + MCU internal

  15. Concepts: Option 4 All electronics and battery internal

  16. Concepts: Option 5 Amplifiers internal

  17. Concept Generation See Handout

  18. Concept Generation Highlights Best Option 350 273 200 153 249

  19. Enclosure Design Nicole Varble and Jason Walzer

  20. 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

  21. Concept Generation- Materials/Manufacturing Process See Handout

  22. 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/

  23. ABS Plastic • Important Notes • Relatively high tensile strength • Glass Transition well above body temperature • Specific Gravity indicates lightweight material

  24. 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 Loctite Spray on Rubberized Coating

  25. Feasibility- Water Ingress Test

  26. 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

  27. Feasibility- Heat Dissipation of Internal Components Tout • 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 Tin h Q t, k

  28. 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

  29. 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

  30. User Interface - Connectors Current Model: Part # EGG 2K 326 CLL Straight-Through Proposed: Part # EEG 2K 326 CLV Right-Angle, PCB mount

  31. User Interface- IP Codes See Handout on IP Ratings

  32. Enclosure Design

  33. Enclosure Design

  34. Enclosure Design

  35. Electronics Design Zack Shivers

  36. Overall System Architecture See Handout

  37. 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

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

  39. Microcontroller See Schematic Page 5 • Microcontroller requires little electronics design • MCU needs: • Clean 3.3V supply voltage • I/O connections • Programming interface (JTAG or BSL) • Oscillator (optional)

  40. HESA Signal Conditioning See Schematic Page 6 Hall Effect + ADC Input Voltage Clamping + + Hall Effect - _ LPF Anti-aliasing filter Reference Voltage

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

  42. HESA Signal Conditioning - Calcs • 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 • Full Swing Digital • 3.0V / 3.3 V * 4096 = 3723 bits

  43. AWB H-Bridges See Schematic Page 7 & 8 • 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

  44. 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

  45. 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

  46. Voltage Regulation • SwitcherPro from TI

  47. Voltage Regulation 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.

  48. 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 SwitcherPROused for design of voltage regulation circuits

  49. 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

  50. Embedded Control System Andrew Hoag and Zack Shivers

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