IMPROVEMENTS IN DIFFERENTIAL PULLEYS OR PULLEY-BLOCKS
Year: 1884

page_text: COMPLETE SPECIFICATION.
I WILLIAM PHILLIPS THOMPSON Fel. Inst. P.A., of the Agency for Foreign Patent
Solicitors, 6 Lord Street, Liverpool in the county of Lancaster, Civil Engineer do
hereby declare the nature of the said invention for " IMPROVEMENTS IN DIFFERENTIAL
PULLEYS OR PULLEY-BLOCKS" and in what manner the same is to be performed,
to be particularly described and ascertained in and by the following statement:-,
This invention has relation to that class of pulleys or pulley-blocks commonly
known as differential pulleys, and the object of the said invention is to produce
a simple, durable, cheap and efficient pulley of the class named, wherein the load
will be held at any point without danger of slipping, the continuous rope or line
wound and unwound without wearing or abraiding one portion against the other
and without unnecessary friction, and on which the rope or line may be quickly
and easily replaced by a new one whenever desired.
To accomplish all of this, the improvements involve certain novel and useful
peculiarities of construction, relative arrangements or combinations of parts, and
principles of operation, all of which will be herein first fully, described and then
pointed out in the claims.
The mere winding and unwinding of a line or chain simultaneously but with
varying rapidity in order to produce the differential resultant movement is
a principle well understood. Heretofore in the construction of pulley-blocks
employing this principle the chain has been commonly employed, and in this form
it is observed that after long use the links of the chain become stretched and worn,
and the-furrows formed in the sheaves become worn so that it is impossible to
substitute a new chain in the old block or adapt a new block to receive the old
chain, in consequence of which the entire device becomes useless as soon as one of
its parts are worn or broken. Where the rope or flexible line has been employed
(in this class), when one part of it reaches the margin of the sheave it rides up
upon the adjacent portion and practically prevents the further hoisting or lowering
of the load, besides producing an excessive wear upon the line. To obviate this it
has been proposed to employ separate and independent lines and also to lead the.
lines about the two sheaves so that parts thereof cross between the axes of the
sheaves, also producing wear, limiting the movements of the load, and rendering it
D

page_text: difficult to replace the line in its intricate windings as well as increasing the cost
of the specially devised sheaves and their fittings.
I obviate these several objections to the differential pulley-block as heretofore
constructed and secure various advantages by the simple construction .and
arrangements below explained.
In the accompanying drawings forming part of this specification, Fig. 1 is a side
elevation of a differential pulley-block arranged for operation in accordance with
the invention and involving the principles thereof, the front plate of the upper or
main block being omitted.
Fig. 2 is a front elevation, and Fig. 3 a central vertical section of the apparatus
shown in Fig. 1.
Fig. 4 is a sectional view of the upper and lower sheaves of the main block
detached from the frame, indicating a variation in the number of grooves in the
sheaves and different ways in which the sheaves may be cast, all within the limits
of the invention; and Fig. 5 is a front elevation of these two sheaves with the line
wound thereon in accordance with the invention.
.
Fig. 6. is a plan of the axles of the two sheaves in the differential block,
showing a slight inclination which it is preferred to give them, one with respect
to the other.
.
In all these Figures like letters of reference wherever they occur indicate
corresponding parts.
A A¹ are the sides of the differential block, which may be of any material and
any size or shape. These plates sustain the axles of the upper and lower sheaves
therein and are connected with any ordinary suspending device as the hook B.
C C' is the upper sheave, and D D¹ the lower sheave, both provided with grooves
to accommodate the rope or line, and both having one section larger or of greater
diameter than the other, as indicated. In each sheave, both sections must move
together, and when the pulley is in operation both sheaves move together. The
relative sizes of these two sheaves (each considered as a whole) may vary to any
extent desired, but it is important and necessary, in order that the line may run
smoothly and properly that the circumferences of the two sections of the two
sheaves shall bear the same relative proportions one to the other, that is, as the
circumference of section C is to the circumference of section C', so must circum-
ference of section D be to circumference of section D!. Without this the line
would not pay on and off the sheaves in the proper manner.
The diameters of the sheave sections are of course in the same proportions as
their circumferences, and these diameters are most conveniently measured by
taking the distance between the centres of the rope-groove at top and bottom of
the sheave.
The rope or line is wound about the two sheaves so proportioned, from outside
to outside of the pair, never crossing between them. The grooves are to keep the
moving portions of the rope free and clear of each other, and it should be observed
that there is one more groove (in which the rope moves) in each of the sections
of the upper sheave than in the corresponding sections of the lower sheave. This
is necessary in the form shown in order that the rope may lead properly, but the
invention is not limited to any relative number of grooves. Of these grooves there
may be two in each of the lower sections and three in each of the upper sections,
or these numbers may be correspondingly increased to any desired extent, though
they cannot be decreased in the form shown, and lead and hold the rope in
accordance with the invention.
The rope
is continuous that is after being properly located in the pulley-block
and in the fall, its ends are spliced; and it may be of any length so as to insure
the proper travel of the fall upon. which the load is applied. It should also be
observed that it is immaterial upon which section of the rope the fall is applied,
inasmuch as both portions are made to move in equal degrees, though for conve-
nience one part is called the hand portion and the other the fall portion.
E represents the rope and F the fall, which may be of any character.
1

page_text: The rope is wound as follows: Starting from any point as (for instance) the
bottom of the loop in the hand portion Figs. 2 and 3, it is carried up over the
outside groove in section C, down under the outside groove in section D, up over
second groove in C, down under second groove in D, up over third groove in C,
down under third groove in D, up over fourth groove in C, down behind to the
fall, up under the fall pulley, over first groove (at the right) in C¹, down under
first in D¹, up over second in C³, down under second in D¹, up over third in C+,
down under third in D¹, up over fourth in C¹, then down behind to the starting
point where it is spliced. The same system of winding is followed in the case
where the lower sheave has only two grooves in each section thereof and the upper
three, as indicated in Figs. 4 and 5, and it is also followed, however the number of,
grooves may be varied.
Being so arranged when one part of the hand portion is pulled down, the fall is
compelled to rise, but with a different velocity, depending upon the variations
between the diameters of the two sections of the upper sheave, upon principles well
understood. By pulling down upon the other portions, the.fall will descend with
like difference in velocity.
The greater the number of grooves in the sheaves the greater will be the
certainty with which the load may be held (without slipping) after being elevated.
The lower sheave is only employed as a guide for the rope and the rope must lead
from one sheave to the other in a slightly inclined direction, as best indicated at
Fig. 5. To obviate any cramping tendency which might result from this
inclination, the axes of the sheaves are located so that they cross each other
substantially as indicated in Fig. 6. These axes are (supposing the pulley to be
suspended freely) in separate planes, and their relative inclinations are very slight,
as indicated.
4
When the pulley is in use one portion of the hand rope runs up loosely to its
groove in the upper sheave, and would be liable to buckle thereon or not lead fairly
thereto unless provided with a suitable guide.
.
To supply this there are employed a pair of light rollers a a mounted upon the
frame of the pulley-block in any light springs as b b, the tension of which may be
adjusted by suitable screws c.
These rollers insure the proper leading of the rope by pressing thereon with
only sufficient power to keep the rope taut and in proper line, but not hard enough
to produce any appreciable resistance to the workings of the pulley.
The sheaves may be of cast metal, and hollow or solid as may be desired. One
made hollow is shown in Fig. 5. They may be cast with the grooves in them and
have only to be cleaned out to be made ready for application.
The construction is found in practice to be simple and well calculated to answer
the several purposes and objects of the invention as previously set forth. If the
rope becomes worn it has only to be replaced by another, which may be quickly
and easily done-or if broken it may be spliced, advantages which will be readily
appreciated. The use of the rope has many advantages over the chain, notably its
cheapness, lightness, greater flexibility and greater ease and smoothness of
operating and of handling.
Having now particularly described and ascertained the nature of the said
invention as communicated to me and in what manner the same is to be performed,
I declare that what I claim is :—
:-
1st. In a differential pulley of the character herein set forth, the upper and
lower sheaves grooved for the reception of the rope, each sheave being composed
of two sections movable together, the sections in the two sheaves bearing the same
relative proportions to each other, substantially as shown and described.
2nd. In a differential pulley the combination with the two grooved sheaves
proportioned as explained, and the fall of the operating rope wound over and
under the larger sections of the two sheaves from outside to outside, under the
fall, and over and under the smaller sections of the two sheaves from outside to
outside, and spliced substantially as shown and described.

page_text: 3rd. In a differential pulley having the two grooved sheaves proportioned as
explained, the rope wound thereon as explained, and the fall, the spring actuated
rollers mounted upon the frame of the pulley block, and serving to guide the hand
portions of the rope, substantially as set forth..
4th. In a differential pulley the upper and lower sheaves grooved for the. 5
reception of the rope, the axes of the two sheaves being inclined with respect to
each other, substantially as shown and described.
Dated this eleventh day of February, 1884.