DoF Analog Ventilator
grabcad
This concept for an analog ventilator aims to address the urgent global need for full-featured ventilators to combat COVID-19. Patients worldwide require similar levels of care, so this design separates its essential functions from resources that vary significantly between countries. Building on the Manley ventilator design from the 1950s, this model allows control of breathing rate, tidal volume, inspiratory pressure, maximum pressure, minimum pressure, and oxygen/air mix ratio without electricity or computer control. Please note that this is purely a concept. This CAD does not represent a ventilator that can be used for patients. The goal is to create a full-featured ventilator that can function in various environments with minimal compromises in functionality. This design avoids the assumption of extensive access to, or familiarity with, computer controls, 3D printing, programming, or other engineering disciplines. For example, this design allows production of critical components using 2D fabrication. The main structure, check valve assembly, bellows plates, and bellows can all be fabricated from sheet material, often the same sheet. The seals and flaps of the check valve assembly are formed from a single sheet of flexible material. This design does not preclude addition of electronics for telemetry, alarms, fault management, or patient-initiated cycling, but these aren't a prerequisite for its successful operation. Operating Sequence: 1. When the bellows are fully extended and the panel is tilted upwards, the top panel contacts the directional control valve toggle, pushing it up (stroke can be adjusted by moving and re-tightening the slider on the trigger bracket). 2. The toggled directional control valve directs pressurized air away from the air cylinder and to the PEEP cutoff valve chamber. 3. Compressed air pushes the PEEP valve cutoff flap against the top of the valve chamber, cutting off airflow from the exhalation line to the PEEP water volume. Meanwhile, ambient air flows through the needle valve into the air cylinder, with the retraction rate controlled by the degree of flow restriction through the needle valve. 4. The panel falls under the weight of the assembly at a rate controlled by ambient air flowing out of the cylinder and through the needle valve. 5. Bellows are pressurized by the force applied by a fixed mass whose mechanical advantage is varied by moving the mass on top of the panel. 6. The mix ratio of air and oxygen is set by the ratio of cross-sectional areas of air and oxygen bellows. 7. Compressed air is toggled between the extension cylinder and PEEP closeoff valve, allowing breathing pressure to vary during inhale and exhale steps. Enhancements over the Manley ventilator include: 1. Using a 2D fabricated Designed Offset Joint to create deterministic 3D motion with a simpler structure. 2. Use of folded bellows to allow creation of highly elastic, geometrically deterministic volumes using largely inelastic materials. 3. Use of two bellows to control mix ratio rather than valve flow rate tuning to control mix ratio. 4. Use of 2D stacked plates and a single sheet of flexible material with cuts and holes to create a valve assembly. Some areas for improvement and forward work: 1. Add locations for easier integration of electronics for telemetry, fault management, alarms, and patient-initiated breathing. 2. The PEEP cutoff valve should be closer to the patient, reducing the amount of exhaled air that could be re-inhaled during the next cycle. 3. Valve assembly needs screws for clamping shut. Plates likely have to be stiff to sufficiently distribute preload, or additional compliant material needs to be added to accommodate displacement of valve plates. 4. Origami bellows do not rigid fold, so some degree of compliance is necessary for folding behavior. It's likely possible to tune the fold pattern such that it extends in an arc rather than linearly. This design was created in Fusion 360 and the uploaded model is v118. V101 eliminated two valve traces in the top plate of the valve assembly in v98. V118 corrected the label for directional control valve inhale/exhale assignment. Thank you to the PEEP valve designer, Smart Water Bottle designer, and weight designer whose models I used in this design.
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