IM- PROVEMENTS IN FRICTION BREAKS AND APPARATUS FOR GIVING MOTION TO MACHINERY
Year: 1866

page_text: PROVISIONAL SPECIFICATION left by Robert David Napier at the Office
of the Commissioners of Patents,. with his Petition, on the 6th November
1866.
I, ROBERT DAVID NAPIER, of 20, Church Row, Limehouse, in the County
of Middlesex, do hereby declare the nature of the said Invention for "IM-
PROVEMENTS IN FRICTION BREAKS AND APPARATUS FOR GIVING MOTION TO
MACHINERY," to be as follows:-
This Invention consists in improvements in the brake patented in August
1861 (No. 3060) by John D. Napier, also in various ways of applying the
same, and in other plans of friction brakes.
In the first part of my Invention the two ends of a brake strap or its
equivalent surrounding or nearly surrounding a wheel are jointed to a lever
in a similar way to those of the Patent brake referred to, that is, the two
joints are on the same side of the fulcrum of the lever; but according to my
Invention the fulcrum in place of being in a permanently fixed position is so
connected to any mechanical appliance that it may be moved through an arc
of a circle whose centre would be that of the brake wheel. The lever to which
the brake band is jointed I call the differential lever, and its fulcrum the
differential fulcrum.
In applying the above arrangement simply as a pall brake (that is, a self-
holding brake which may be slacked when desired) a stop is introduced in
such a position as to limit in one direction the movement of the fulcrum in
the before-mentioned arc, and to make any further movement in that direction
release the pressure of the brake band on the wheel.

page_text: The next part of my Invention consists in adaptations of the self-holding
arrangement described for the purpose of communicating power and rotary
motion to machinery. By one adaptation I obtain an improved purchase
applicable to windlasses and other hoisting machines, and to other
purposes, such as the screwing down of screw piles or the turning of drilling
braces in place of the usual ratchet and pall, and by another arrangement I
obtain an improved friction clutch especially suited for rolling mills and other
heavy machinery that has to be suddenly thrown into gear. For the hoisting
purchase of a windlass I use a hoisting brake which is on the plan described,
and also a pall brake or palls, or a second hoisting brake. The movement of
the differential fulcrum of the hoisting brake in one direction turns the wheel
and raises the weight some distance, when a reverse movement lets the other
brake or its equivalent take the strain and slacks the hoisting brake strap,
which is then pulled backwards for a fresh grip, when the hoisting is repeated ;
when there are two hoisting brakes they are generally used alternately. To
obtain what I call a differential friction clutch the pin of 'the differential
fulcrum is fixed in a crank or wheel which revolves round the same central
line as that of the brake wheel which may either be the driving or the driven
wheel, and various methods may be adopted for throwing the clutch into or
out of gear.
Another part of my Invention consists in other modifications of differential
brakes suitable for cases where it is inconvenient to have a band surrounding
the wheel which acts as the brake wheel, such, for example, as when applying
brakes to railway carriage wheels.
In these modifications a segment of a ring, which I call the brake segment,
takes the place of the brake band, and it may be about half or any smaller or
larger portion of a ring. The two ends of the brake segment are jointed to
links of which the other ends are jointed to a lever at different distances
from the fulcrum. These joints correspond in some respects to the joints
of the band in the brake patented by Joh D. Napier, as already referred
to, but in these arrangements the joints are on different sides of the
fulcrum of the lever, which when nearly straight is placed nearly at right
angles to a radius from the centre of the brake wheel to the fulcrum, in
place of being nearly in a line with such radius as in other cases.