Biomimetic Vibration Damping
for a movie soundtrack reader
front
rear


This soundtrack reader design replaces the rigid arms, bearings, coil springs, and dashpot of normal readers with arms that are beam springs and blocks of viscoelastic foam for damping.

These are the advantages:

  • replaces over $40 of parts with less than $5 of parts
  • uses less material
  • requires far less maintenance and repair
  • when maintenance or repair is required, it is much faster and cheaper
  • in my lab tests it can dampen vibrations up to 5% better

    Details

    Soundtrack readers on movie projectors must minimize vibration in the film in order to avoid errors while reading the soundtrack data printed on the film. All vibration damping in movie projectors is done by passing the film over a high-inertia drum, with sprung rollers that constantly take up the slack in the film before and after it passes over the drum. Most soundtrack readers have these rollers on rigid arms pivoting in low-resistance ball bearings, with two coil springs and a dashpot in order to take up the slack and thus dampen film vibration.

    As a fan of biomimicry, I looked to nature for a better solution. While animals often have rigid arms that rotate at joints, they generally do not use them to absorb constant vibrations. A better analog to the problem that we need to solve would be trees bending in the wind. Trees do not have pivoting joints; instead they flex all along the length of their arms. They also do not have dashpots or springs; instead, their wood is like a structured foam that distributes forces throughout it. Finally, most natural structural foams like wood rebound at a much slower rate than they are impacted, making them viscoelastic for effective absorption of impact or vibration. My design has arms which flex along their whole length (they are beam springs) and which use viscoelastic foam ("memory foam") for damping. This makes it mechanically simpler, cheaper to manufacture, easier to maintain, and perform better.

    This design requires foam blocks on the distal ends of the damping arms, to avoid roller misalignment from the beam springs' low torque resistance. However, this does not interfere with operation or film threading, and is included in the cost estimate above.