Mechanical Specifications

Plumbing

Calculations

Overview

This section details the construction of the mechanical assembly of the ventilator. Simplicity and accessibility of commercial-off-the-shelf (COTS) components are emphasized. This design philosophy enables a highly modular and maintainable system. Any one part is easily swappable and likely already exists in a nearby hobbyist's or hardware store's inventory.

Physical Characteristics

Physical Characteristics

Characteristic

Measurement

Max Footprint (L, W, H)

14" x 15.5" x 17" / 356 x 394 x 432 mm

Touch Screen Size

6.1” x 3.4” / 155 x 86 mm

Weight

17.5 pounds / 6.4 kg

Noise Level

60-70dB (Operating) / 88dB (Alarm)

Supported Languages

English

There are no rows in this table

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Device Frame

The frame of the ventilator is designed entirely from 80/20 aluminum extrusion. This robust and versatile material is commonly available to buy in large quantities, and can easily be substituted with other extrusion types that support T-nuts. The entire frame is assembled with angle brackets and hex-head bolts, allowing construction with a single Allen key. The Ambu-bag slots between two beams of 80/20 extrusion, 4" apart, and is secured using two U-bolts that can easily be raised and lowered with thumbscrews to switch bags. The U-bolts can be adjusted back and forth, as well as up and down, to ensure a secure fit for a variety of Ambu-bags. Two handles on the left and right sides allow for easy transportation.

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Compression Arm

The hinged compression arm consists of an 80/20 aluminum extrusion and is pulled down using a rope to compress the Ambu-bag. An eyebolt at the end of the arm secures the end of the rope in position.

The end effector of the arm approximates a crescent shape to compress the Ambu-bag without sharp edges, mimicking compression by a human hand as to avoid shortening the lifespan of the bag. This is accomplished with a set of two eccentrically crescent-shaped door handles. An extension spring attached between the back of the arm and the frame of the device allows the arm to passively hinge back to its original position.

This design, centered around a single moving arm, was chosen because it delivered tidal volume most consistently (close to linear), was easily integrated into a COTS solution, and maximized mechanical advantage.

The compression arm is able to fully hinge horizontally, compressing the Ambu-bag completely. This easily accomplishes the desired amplitude range of 0 to 6 inches of compression, as well as the tidal volume requirement of 200 to 800 mL specified by consulting medical professionals.

Motor Selection

VentCU's actuation is powered by a bipolar NEMA 23 stepper motor with a built-in encoder, 1.95 N-m (276 oz-in) of holding torque, 1.8° step angle, and 200 steps per revolution. It draws 2.8 A under full load and is rated to run at 12 V, producing up to 34 W of power. To safely ensure that the motor does not fail under continuous usage, this amount of power is 6W greater than the required amount of 28W. A timing pulley with a pitch diameter of 1.5" is affixed to its output shaft, providing an output tension force of 200 N (45 lbf) on the rope pulling down the arm. This stepper motor can spin at 400 revolutions per minute with maximum holding torque, leading us to believe it could achieve the desired respiratory rate of between 10 to 30 breaths per minute.

However, upon experimental testing, we discovered the motor was unable to reach the desired respiratory rate at certain inspiration to expiration ratios. This is due to the motor being under-torqued. A more powerful motor should be selected and tested to ensure the device meets the required specifications. This is further detailed within

Limitations & Future Work⁠

Next:
`Electrical Specifications`⁠
|
`Overview`⁠
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