IMPROVEMENTS IN PULLEY BLOCKS FOR RAISING AND LOWERING WEIGHTS OR HEAVY BODIES
Year: 1872

page_text: PROVISIONAL SPECIFICATION left by Thomas Henry Ward at the
Office of the Commissioners of Patents, with his Petition, on the
5th July 1872.
I, THOMAS HENRY WARD, of Smethwick, in the County of Stafford,
Mechanical Draughtsman, do hereby declare the nature of the said
Invention for "IMPROVEMENTS IN PULLEY BLOCKS FOR RAISING AND LOWERING
WEIGHTS OR HEAVY BODIES," to be as follows:-
My Invention consists in constructing and arranging the parts of the.
said pulley blocks in the following manner:-The axis upon which the
rotating parts turn is fixed in the supporting frame and is incapable of
rotation. On one end of this axis the sprocket or hand wheel for raising
the load turns the said hand wheel, having on its inner face a short
cylindrical bush or collar situated excentric to the axis of the hand
wheel. Upon this excentric bush or collar a toothed wheel works, the
said excentric bush or collar turning within the toothed wheel. The
said toothed wheel is surrounded by a concave or hollow toothed wheel
which is cast or made in one piece with the load wheel. A second or

page_text: lowering sprocket wheel is situated at the opposite end of the axis to
that at which the first or lifting sprocket wheel is situated. This second
sprocket wheel has a long cylindrical bush or collar, that part of the
said bush which is situated at the middle of the frame being excentric.
Upon this excentric bush of the second sprocket wheel the load wheel
with its hollow toothed wheel turns. The opening in the load wheel is
excentric to the periphery of the said load wheel, its excentricity being
equal to that of the bush on which it turns. The opening in the middle
of the toothed wheel is in part cylindrical, and in part hexagonal, or of
other angular figure. That part which is cylindrical works upon the
short excentric bush of the first sprocket wheel, as already described,
while the hexagonal portion is occupied by a hexagonal nut considerably
less in size than the hexagonal opening in the toothed wheel, the said
hexagonal nut being secured to the fixed axis of the pulley block.
In using the pulley block for raising a weight, the second or lowering
sprocket wheel is turned into such a position that its excentric bush
brings the load wheel concentric with the axis of the pulley block. In
this position the teeth of the toothed wheel working on the excentric
bush of the first sprocket wheel engage with the teeth of the hollow
toothed wheel. By now working the lifting sprocket wheel the toothed
wheel is carried round the hollow toothed wheel, but is incapable of
rotating in consequence of one of the planes of its opening always being
in contact with one of the planes of the fixed hexagonal nut. As a
consequence the hollow toothed wheel and with it the load wheel rotate
the said hollow toothed wheel advancing on each rotation of the lifting
sprocket wheel through a distance equal to the difference between the
number of teeth on the toothed wheel and those of the hollow toothed
wheel: During the rotation of the load wheel it carries the second or
lowering sprocket wheel with it, and the concentricity of the load wheel
with the axis of the pulley is thus always preserved. In order to lower
the weight the lowering sprocket wheel is turned so as to bring its
excentric bush concentric with the excentric bush on the raising sprocket
wheel, and also into such a position with respect to the excentricity of
the load wheel that the toothed wheel shall be disengaged from the
hollow toothed wheel. When the parts are in this position the load
wheel may turn through a certain angle, but owing to the excentricity
of its bush it soon brings the hollow toothed wheel again into gear with
the toothed wheel, and its motion is arrested.

page_text: In order to permit the descent of the load the two sprocket wheels
must be simultaneously moved so as to keep them in the relative position
described for disengaging the load wheel.
By preserving the relative position of the parts described, the weight
may be lowered to the desired extent.
In order to prevent the overloading of the pulley I suspend the frame
by means of a rod, an angular portion of which works in an angular hole
in the top of the pulley frame. The lower end of this rod carries an
arm which projects within the lowering sprocket wheel. Surrounding
the rod and between the said arm and the under side of the top of the
frame is a strong coiled spring, the strength of which is so adjusted
that when it is attempted to raise a greater weight than the pulley is
calculated to carry, the said spring is so far compressed as to cause the
arm described to bear against the interior of the lowering sprocket wheel,
and to gag the said wheel and prevent the action of the pulley.