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Leonardo
da Vinci also recognized the difference between static and sliding friction
and the advantage of using rolling contact in a rotary bearing. The sketches
on a page from Codex Madrid show several bearing designs. At the top is a
simple pivot design which locates the conical end of the shaft in a group of
three balls confined by a cup-shaped race. Ideally, only point contact occurs
between the balls and the race and the shaft and the balls.
An alternate
design shows the same shaft located by conical rollers that are located
by a conical race. The roller and race design avoids sliding contact between
the conical rollers and the race, and only line contact is made between these
components. Line contact also exists between the rollers and the shaft.
The
lowest designs show systems with even more constraints. The rollers
are located by shafts which must then run in bearings to minimize friction
losses and the lower conical "plane bearing" will make an area contact
between the conical shaft and the bearing.
In all designs, lubrication
is an advantage and the records indicate that animal fats were used for
this purpose. |
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