Page 146 - Anatomy of a Robot

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RELIABILITY, SAFETY, AND COMPLIANCE 131
MECHANICAL THREATS
An interesting story comes to mind, so far uncorroborated. Coal power plants have had
a problem matching their power generation to the required loads. Coal fires take a long
time to burn out, so energy can be wasted in the evening hours as people retire for the
night. Power companies have been looking for ways to store the wasted electrical energy
so it can be reused the next morning.
Clever designers decided to investigate putting the energy into a flywheel. The fly-
wheel was to be a large rotating wheel driven by a motor/generator. In the evening, they
would speed up the flywheel to store up some of the wasted energy from the coal fires.
In the morning, the flywheel would spin the generators to reclaim the energy before the
coal fires were completely burning. The flywheel was to be massive, an intimidating
hunk of spinning concrete and steel. Clearly, if the flywheel ever came loose, it would
be quite dangerous. The design plan was to set the flywheel on the edge of Long Island
Sound, a 10-mile wide body of water between Long Island and Connecticut. If the fly-
wheel ever broke loose, it would roll into the water and thus dissipate its energy.
Calculations showed it would only get three-quarters of the way across to the
Connecticut shore before it rolled to a stop! I’m guessing this information was cold
comfort to the beach residents in Connecticut.
In general, inspect the robot design for places where energy is stored. It does not take
much energy to create injury or to cause a breakdown in operation.
The following is a list of items to check for and help avoid mechanical problems:

Leverage Even a small force can be greatly magnified with leverage. Inspect
the robot design for hazards that might be created by excessive leverage or force.
Such hazards probably require shields to prevent accidental injury.
Sharp parts If the robot does not require sharp-edged parts, round them off in
the design phase.
Fast moving parts Even lightweight parts can cause injury if they move fast.
Shielding or redesigning the relevant parts might be in order.
Stressed parts Parts put under stress might break catastrophically. Portions of
the part may fly off. Examine all parts of the design for hidden stress and at least
understand what happens should the part break.

SOUND PRESSURE SAFETY
The human ear can only withstand certain sound pressure levels before injury occurs to
the ear. If portions of the robot are to be noisy, then either calculate the predicted noise
level or measure it directly.