Final Design

CAD drawing of stethoscope cover dispenser

Main components:

    Sticker

A thin (3.5 mil) PET sticker in the shape of a tear drop, this cover sticks onto a stethoscope diaphragm to prevent direct contact with human body. It adheres firmly in place during the examination yet remains easily pealed off without leaving any adhesive residue. The sticker, being acoustically matched to a typical stethoscope diaphragm, transmits sounds with high fidelity, more than sufficient for accurate clinical judgments. Neither the PET sticker nor the silicone adhesive is a source of skin irritation. 

    Receiving spool

This aluminum spool holds onto the free end of the tape roll, held initially by a sticker, it remains durable enough to withstand the high tension in the tape due to the friction between wound tape layers. A small handle is gear reduced in a 4:1 ratio so that the user exerts minimal force while turning around only one revolution.

    Dispensing spool

This plastic spool uses a fin structure to securely bite into the packaged paper ring of a sticker roll, providing enough force to fix the tape while maintaining convenience when replacing empty rolls. A ratchet and pawl system is included to generate enough friction to keep the spool from rotating too much and slackening the tape.

    Bullnose

The bullnose is composed of an S-shaped plastic top with a plastic bottom plate, separated by a 3.5 mil gap, to generate enough tension in the tape to dispense the sticker. The bottom plate extends out to form a tray on which the dispensed sticker sits, and is wrapped with a layer of Kapton tape to generate electrostatic attraction between the sticker and the tray, ensuring that the sticker remains flat when dispensed. A roller wrapped with rubber is placed right above the bullnose to press onto the tape and ensure a tight turn at the edge to prevent the sticker from flipping backwards onto the tape. The other roller above the dispensing spool bends the sticker in the direction that again prevents the flipping action.

    Case

Thin acrylic sheets with jigsaw patterns form the casing of the device. A slot is cut on the side where the sticker dispenses, while both this and the wall opposite the handle can be disassembled to provide room for replacing tape rolls. The latter features z-links that allow the wall to be pulled out initially then shifted to the side, preventing any conflicts with the shafts.

Performance:

The sticker is capable of high fidelity transmission of sound from 30 Hz to 8000 Hz, the range of clinical interest, with at most a 60% loss at low frequencies and, that only occurring rarely. The sticker also transmits sounds at a larger volume (essentially an amplifier) at other frequencies, occurring about as often as the losses. Overall, clinical judgment is not impeded, as attested by doctors who have tested the product. The bullnose provides sufficient tension on and bending of the tape to ensure 100% dispensing of the sticker, while the receiving spool can withstand that amount of tension without malfunction.

Future Improvements:

Future improvements include shaping the sticker into a tear drop shape for easy handling, making a foldable tray to fully enclose the device, replacing the aluminum receiving spool with a plastic press-fit spool like the bottom, and adding a wall-mount design to the casing. Finally, the device can be automated, in which a motor dispenses a sticker upon receiving motion-sensing input from the user.