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C13A1 Prototype Build Review

Concept C13A1 - Prototype Build Review

@jd18 15 APR 2020

Positive Comments

  1. Many Design Criteria Met

    • Must squeeze bag with sufficient volume displacement
    • Must avoid friction between mechanism and bag to lowest degree
    • Must accept placing the bag (Transition from pumping to loading) or a port for manual bag transitions.
    • Must be able to be sterilized and/or used in a sterile environment
    • Must be able to be on it’s own cart or hang from IV Stand - solve limited table space.
    • Must be able to replace BVM or similar core pump with ease.
    • Must protect the bag from accidental contact from bumps, drops, other equipment
    • Must have the ability to disassemble easily for repair/cleaning
    • Must be able to reach volumes of 1000 per day in industrial facilities
    • Must use as few parts as possible
    • Must Be physically robust enough for rough handling

  2. Overall Look/Feel is quite professional, likely to be acceptable to reviewers, easy to CNC.

  3. Safety and Cleanability strong positives

  4. Dual motor design allows widely available Nema17? and alternates

Neutral Comments

  1. Design Criteria in Question
    • Must have low friction bearings on any high frequency rotating components
      • Gears as drawn work in FEA but printed gears are long prints or need post-processing to survive millions of cycles. Could be milled or molded.
      • Lubrication is a question - and an approval liability.
    • Must have an easy and apparent control interface
      • n/a Where would you propose the control hardware and UI live? Presumably on the front below the platform.
    • Must have simple adjustment for on the fly volume/displacement changes on the device
      • n/a today, but presumably via UI later.
    • Must have simple adjustment for on the fly pressure changes on the device
      • n/a today, but presumably via UI later. Challenge in this design without in-patient-line pressure/flow readings.
      • Feeding back force on the jaws may not be direct enough, also a challenge to be highly accurate
    • Must have a small pole or other Beacon indicating alarms and continuous function
      • n/a today. where would we put this?
    • Must allow sensing for key MVP Specs
      • presumably these sensors are external. wire management? Control interface? Digital readouts?
    • Must allow for sensing of current actuator location / bag displacement
      • n/a today

Next Iteration Challenges

  1. Mechanical core needs reliable control
    • How non-linear is delivered P/V? At what points in the cycle?
    • What about high P/low V and high V/low P? Are there points in the cycle best suited for these modes?
    • How does it deal with extreme back-pressure transients (patient cough, tube kinked, e.g.)
    • How does it deal with extreme force feedback (mechanism binds, user leans on it e.g.)
      • presumably the stepper will just skip steps but needs that per-cycle reset that has been discussed.
      • what happens when set max P is exceeded? Do the jaws back off? Reset?
    • Would any of these specs improve with a second pair of Jaws?
    • Can bag displacement be sensed?
    • Best way to sense gear/motor position?
    • How to best coordinate/fix errors between the two motors? Could just deal with that in code.
  2. Cost / Complexity
    • Current design approach requires pressure and flow sensing in the patient breathing line for Reg Approval, or so we believe.
      • Medical-grade Flow sensors may be expensive (XXX euros/dollars?) and may be in difficult supply chains (global push to build vents)
      • Custom Flow sensors would need significant testing and sterilization protocols for approval
        • and likely require multiple pressure sensors, even more complexibility and liability.
    • Real-time sensor feedback to squeezer position/force/speed may be non-linear and therefore per-breath control may be all that's safe e.g. feedback changes settings for the next breath cycle, more of a calibrated look-up table for settings than a real control loop.
    • Can a lookup table be trusted to replace in-line pressure/volume sensing, eliminating the sensing/regulatory challenges?
    • What's the Mass Production method of choice for the drive train?

Team Lead(s):

Team Gitlab Slack
Acme @jd18 @ Jonathan Kemp