Improvements in Self-sustaining Pulley Blocks
Year: 1896

page_text: Date of Application, 4th June, 1896
PROVISIONAL SPECIFICATION.
Improvements in Self-sustaining Pulley Blocks.
ROOKES EVELYN BELL CROMPTON. Engineer, and EDMUND ARTHUR
NORMAN POCHIN, Engineer, both of Arc Works Chelmsford, England do
hereby declare the nature of this iuvention to be as follows:-
Our invention relates to self sustaining pulley blocks i.e. those which by a clutch
mechanism prevent the falling of the weight that is being raised and sustain it in
position even if the cord or chain be suddenly released or if it is broken at any
point other than exactly between the wheels of the clutch. Such self sustaining
pulley blocks can either be used as the upper fixed block or as a lower moving
block attached to the object that is to be raised and the hoisting device may be the
form of single double or manifold purchase. For convenience of description we
first take the case of a single purchase block attached to the object to be raised.
This pulley block consists of two pulley wheels or sheaves these are mounted at
the two ends of a pivoted lever the sustaining cord passing under these sheaves and
raising them together with the lever attached by the frame in which it is pivoted
to the weight as the sustaining cord is wound up. The pivoting in the frame is so
arranged that the lever has a stable position only so long as the weight is nearly
evenly distributed between the two parts of the sustaining cord. Should one of
these parts break and the weight begin to fall the lever will be tilted by the
pressure of the uninjured cord and that end of it will be raised and thus bring into
action a safety clutch which grips the unbroken portion of the cord and prevents
further descent of the weight. The clutching device consists of a projection
formed on the lever and having a suitably formed surface to act as a gripping
face e. so shaped that the tilting of the lever will bring this surface closer to a
fixed block attached to the frame which we call the anvil and so cause the
sustaining cord to be gripped in this reduced space. This clutch device will work
in either direction so that the fracture of either part of the sustaining cord will
bring it into action and cause the weight to be sustained by the unbroken part.
In one method we pivot the lever on two pivoting centres these two centres being
spaced equally on either side of the centre of the effective length of the lever the
object of this being to prevent the clutch being too sensitive and the sensitiveness
of this device may be varied by making the distance between these two centres
adjustable. In cases where we use this self sustaining pulley block as a safety
device in connection with the raising and lowering of electric lamps such lamp may
be provided with suitable contact pieces or terininals so arranged in respect to
corresponding contact pieces connecting with the wires conveying the electric
currents to and from the lamp that in such cases when our clutch comes into
effective operation suitable switching arrangements will take place cutting the lamp
in or out of circuit if such is found desirable such connection may in some cases be
conveniently operated by the tilting mechanism above described; similarly the
tilting of the lever may be arranged so as to operate suitable electrical contact and
thus ring an alarm bell or exhibit a visual signal or it may be made simply to show
a coloured disc and thus attract attention to the fact that the clutch has come
into operation. Although we have described the clutch pulley as attached to the
weight itself yet it may be used at any point where the sustaining cord changes

page_text: direction such as the upper or fixed block or a fair leading block on any hoisting
system.
Dated this Fourth day of June 1896.
ROOKES EVELYN BELL CROMPTON.
EDMUND ARTHUR NORMAN POCHIN.
We ROOKES EVELYN BELL CROMPTON, Engineer, and EDMUND ARTHUR
NORMAN POCHIN, Engineer, both of Arc Works, Chelmsford, England, do
hereby declare the nature of this invention and in what manner the same is to
be performed, to be particularly described and ascertained in and by the following
statement:-
Our invention relates to self-sustaining pulley blocks; i.e., those which by a
clutch mechanism prevent the falling of a weight, during the time that it is being
raised, suspended, or lowered, which sustain it in position even if the suspending
cord, or chain, be suddenly released, or if it is broken at any point, other than
exactly between the wheels of the clutch.
Such self-sustaining pulley blocks can either be used as the upper fixed block,
or as the lower moving block attached to the object which is to be raised, and
the hoisting device may he in the form of a single, double, or manifold, purchase.
For convenience of description we first take the case of a single purchase block,
attached to the object to be raised.
Figure 1 shows in side view, and Figure 2 in end view, such a self-sustaining
arrangement. Let A. A be a cover plate, or part, of the framework of the object
to be raised and which carries two pulley wheels 61 62 free to revolve in their
respective bearings c'c, these bearings are formed at the two extremities of a
pivotted lever d, the sustaining cord passing under the sheaves b' 62 in the manner
shown in the drawing. The lever D is pivotted in the frame A, at the t:vo
points f,, so long as the weight is evenly distributed between the two parts of
the sustaining cord e e, the lever d remains in the position as shown in the
drawing; that is to say, the weight rests equally on the two pivots ff; if how-
ever either side of the sustaining cord should break, then the lever d no longer
maintains the stable position shown in the drawing, but the pivot nearest to the
unbroken part of the sustaining cord then becomes the centre of motion and the
lever vibrates round this point moving through a certain distance in the curved
slot g, and thus brings the curved face down on the top of the cord e and grips
said cord between itself and the upper face of the anvil block i. Similarly it will
be seen that the breaking of the left hand sustaining cord would reverse these
motions, the pivot f' would then become the centre of motion, the pivot f moving
in the curved slot and the other end h¹ would press on the cord and compress it
between itself and the opposite corner of the anvil block . In either case the
compressing of the sustaining cord, between the lower face of the vibrating lever
and the anvil block, will be sufficient to grip the sustaining cord and so maintain
the lamp, or other suspended article, from falling.
In cases where we use this self sustaining pulley block as a means for raising
and lowering electric lamps, or heating apparatus, or other electric mechanism, in
which it is an advantage for the energy to be switched off if an accident should
happen to the suspension of the lamp, or other device, we can so prolong, or extend
the respective corners h and ', i and of the vibrating lever and the anvil block
respectively, that at the time the lever begins to vibrate, (due to the breaking of

page_text: one of the cords) the pair of corners, opposite to those compressing the suspending
cord, will, by their act of separating themselves open a switching device, which
may be in the form of a single tongue of conducting material, which in the normal
position rests hetween a pair of springy jaws, also made of conducting material, but
which tongue when the two corners are pulled further apart separates from the
jaws to a sufficient extent to shut off the current. This make-and-break contact
device, depending for its operation on the vibration of the lever, may either switch
the current from the apparatus itself completely out of circuit, or it may, by
making contact on the same side as the compressing action, complete an electric
circuit and so ring an alarm bell, or put into action the electric magnet controlling
a visual signal, or controlling a coloured disc, or other device, to attract attention.
Although we have described the double clutch-pulley as attached to the weight
itself, yet it may be placed overhead attached to a fixed support, in which case the
arrangement would be turned upside down; or in cases where the strain is brought
on to it in a sidewise direction, as when the cord passes round it, merely to change
its direction, it may be fixed at any convenient angle: but in all cases the principle
remains the same the two pulleys carried by their vibrating lever resting under
normal conditions on the two pivots ff and the lever vibrating as above described
in case of one part of the cord breaking.
Having now particularly described and ascertained the nature of our said inven-
tion, and in what manner the same is to be performed, we declare that what we
claim is :-
1. In safety hoisting devices, the use of a pair of pulleys, mounted on a vibrating
lever having two pivots, substantially as and for the purposes herein described.
2. In safety devices more particularly used for suspending, or maintaining in
position, apparatus for utilizing electricity, in combination with the safety
sustaining mechanism of an electrical contact, by which its action may be notified,
either by switching off the current or by causing an aların, substantially as set
forth.
Datashe 2nd day of March 1807
WM. BROOKES & SON,
55 & 56 Chancery Lane, London, Agents for the Applicants.