IMPROVEMENTS IN APPARATUS FOR RAISING AND LOWERING HEAVY BODIES
Year: 1877

page_text: PROVISIONAL SPECIFICATION left by Alfred Todd at the Office of the
Commissioners of Patents on the 18th January 1877.
ALFRED TODD, of Birmingham, in the County of Warwick, Mechanical Engineer.
"IMPROVEMENTS IN APPARATUS FOR RAISING AND LOWERING HEAVY BODIES."
My Invention consists of the improvements herein-after described in apparatus
for raising and lowering heavy bodies, which improvements are in part applicable
to an Invention for which Provisional Protection has been granted to me dated
November 17, 1876, No. 4452, and are in part applicable not only to my Invention
already provisionally protected, but also to other apparatus for raising and lowering
heavy bodies of the kind commonly called differential pulleys.
In order to press the ropes or chains of pulleys tightly into the groove or grooves
of the pulleys, and thereby prevent the said ropes or chains from slipping, I mount
a small roller upon the end of a short arm jointed to the frame of the pulley, the
said roller being situated near the side of the pulley opposite to that at which the
load is suspended. By means of a spring the said roller is made to press upon the
rope or chain, and force it so tightly into the groove of the pulley that slipping is
prevented.
When two pulleys are situated over one another, the two jointed arms may be
pressed towards the peripheries of the two pulleys by the action of one coiled or
other spring. In place of a spring, a weight may be employed to press the rollers
on the rope or chain.
In some cases it is desirable to make the action of the pressing rollers automatic,
that is, to bring them into operation by the action of the weight suspended to the
pulley with a force proportionate to the suspended weight.
In this case I cause the
rope or chain of the loop in which the snatch block carrying the weight is hung to
pass between two grooved rollers carried by a nearly horizontal arm, the position of
the said rollers being such that when the arm carrying them is in its normal position
the cord or chain passing between them is deflected out of a vertical line. The arm
carrying the rollers is capable of turning upon a centre coincident with the axis of
the pulley, and the tension put upon the deflected cord or chain by the suspended
weight tends to straighten the said cord or chain, and in doing so to turn the arm
carrying the rollers upon its centre. This arm is so geared with a pressing roller or
pressing rollers that the motion given to it by the straightening of the cord or chain,
Price 2d1

page_text: causes the said pressing rollers to press the cord or chain into the groove or
grooves of the pulleys. The heavier the suspended body the nearer is the deflected
cord made to approach a straight line, and the greater the pressure of the rollers
upon the cord or chain. By means of a cord or chain attached to the end of the
arm it can be restored at pleasure to its normal position, and the pressure of the
rollers be removed from the rope or chain.
The several arrangements described for pressing the rope or chain into the groove
or grooves of the pulley are applicable to the Invention herein-before referred to
and provisionally protected by me, and also to differential pulleys generally.
Where it is thought desirable to have a great range of power in pulleys of the
kind already provisionally protected by me I modify the said pulleys in the fol-
lowing manner:-
:-Instead of gearing the two sheaves together directly I gear them
together by means of an intermediate toothed wheel. By applying a winch to this
intermediate wheel or making it into a worm wheel and driving it by a tangent
screw great additional power is obtained.
I prefer in all cases to corrugate the groove or grooves of the pulley in order
thereby to give the rope or chain a greater grip or hold thereon.