Year: 1896

page_text: Date of Application, 3rd June, 1896
Complete Specification Left, 2nd Mar., 1897-Accepted, 17th Apr., 1897
I, WILLIAM ERNEST DALBY, of the Engineering Laboratory Cambridge University
Demonstrator in Mechanism and Applied Mechanics in the University of Cambridge
do hereby declare the nature of this invention to be as follows:-
My invention consists in improvements of that class of transmission dynamometers in
which the torque or driving effort, between one shaft & another is proportional to the
relative angular displacement of two pullies, or pieces connected by a spring, & the
improvements consist of mechanism, whereby this relative angular displacement can
be conveniently measured, without transmitting the power through the measuring
mechanism.
For this purpose I employ two measuring pullies of the same diameter, fixed
co-axially to the two shafts, pullies, or pieces, whose relative angular displacement is
to be measured. Over these measuring pullies, a continuous band chain, or any
wrapping connector; hangs in two loops, & in each of the hanging loops, is placed a
guide pulley. The chain or band is placed on the pullies in a similar inanner to the
arrangement of the chain in a differential pulley block, or in such a manner as will
produce the motion I require.
When the shaft is running, so long as there is no relative angular displacement of
the measuring pullies, the loops of the band remain at the same distance apart.
Relative angular displacement of the measuring pullies causes the loops to approach,
or recede from one another.
The guide pullies hanging in the loops are constrained to move vertically without
side play or swinging, in a fixed frame.
The relative linear displacement of the guide pulleys is directly proportional to the
relative angular displacement of the measuring pullies.
The relative linear displacement of the guide pullies is measured by a pointer or
index finger attached to the one, indicating readings on a scale attached to the other.
By suitably calibrating these readings the torque may be at once inferred.
The form of band I prefer is a steel tape punched with holes at regular intervals,
so that it may work evenly over toothed measuring pullies, or sprocket wheels, to
prevent slipping or creeping.
Instead of letting the loops of the band hang vertically, I may use them horizon-
tally, controlling the motion of the guide pullies, & keeping the required tension on
the band, which before was supplied by the weight of the guide pullies; by suitably
arranged springs.
In one arrangement I use a spring so connected to the guide pullies & controlling
their motion, that for any variation of the distance apart of the centres of the guide
pullies, the tension on the spring remains constant.
The frames which carry the guide pullies are constrained to slide along the fixed
guiding bars in the fixed frame, by the constraint caused by the contact of 6, or even
more, properly chosen points of contact between the frame & the guiding bars.
Dated this 2nd day of June 1896

page_text: Improvements in Transmission Dynamometers.
I, WILLIAM ERNEST DALBY Professor of Mechanical Engineering & Applied
Mathematics, of the City & Guilds of London Technical College Finsbury London E.C.
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:
My invention consists in improvements of that class of transmission dynamometer
in which the torque or driving effort between one shaft and another, or one pulley and
another, is proportional to the relative angular displacement of two pullies or pieces
connected by springs; and the improvement consists of apparatus whereby this relative
angular displacement can be conveniently measured, without transmitting the power
through the actual measuring mechanism.
Fig. I Sheet I exhibits one way of using my invention. One end of the spring S is
fixed to the shaft A, and the other to the pulley B. The shaft A drives the pulley B
through the spring S. The pulley B is not keyed to the shaft, but is free to turn on
the shaft, but for its connection to the shaft by the spring S. To minimise friction
between the pulley and the shaft I mount the pulley on ball bearings, but I may use
any form of bearing I find convenient.
If the torque on the shaft differs at any instant from the torque at the pulley, that
is if the driving effort differs at any instant from the resistance, there will be relative
angular displacement between the pulley and the shaft, the spring twisting or untwisting
until equality between the driving effort and the resistance is established.
To measure this change in torque it is necessary to measure the relative angular
displacement of the two ends of the spring, that is of the shaft A and the
pulley B. To do this I fix a sprocket wheel Q, to the pulley B, and I fix another
sprocket wheel Q, of the same diameter as the sprocket wheel fixed to the
pulley B, to the shaft A. Over these sprocket wheels I place an endless band E
punched to correspond with the sprocket wheels. The band forms two loops. The
parts of the band forming one loop lead to opposite sides of the two pullies as shown
in Fig. 2. In the two loops thus formed I place guide pullies, suitably constrained to
prevent sideways oscillations, and to follow the motion of the loops. Relative angular
displacement of the two sprocket wheels is necessarily accompanied by a change of
the distance apart of the loops. The relative linear displacement of the guide
pullies therefore placed in the loop, is proportional to the relative angular displace-
ment of the sprocket wheels and therefore is proportional to the twisting of the
spring S Fig. 1. Sheet 1.
I use a scale fixed to one guide pulley frame reading against an index fixed to the
other guide pulley frame to measure this relative linear displacement. In Fig. I
Sheet 2, K is the scale attached to the frame F, and I is the index attached to the
frame F.
By suitably calibrating the scale readings, change in torque may be read off
directly.
The form of band 1 prefer is a thin steel tape punched at intervals so that it may
work evenly over the sprocket wheels-but I do not confine myself to this particular
form of band or this particular material I may use a chain or a cord or a wrapping
connector of any form.
To prevent sideways oscillation of the guide pullies in the loops, I mount them in
frames and guide their motion by means of three bars B, B, B, Figs. 3 and 4. I
arrange the frames so that each frame has five points of contact with two
bars of the group of 3 bars. These points are numbered 1, 2, 3, 4, 5 in
Figs. 3 and 4 Sheet I. These points are maintained in contact by the spring S₁ and

page_text: piece P. As will be seen from the drawing the points of contact are obtained by
forming two V's on the frame; V, V, and arranging that the frame touches the bar B,
at the one point 5.
The frame shown in Figs. 3 and 4 Sheet 1 is the form I may use if the loops hang
vertically, but any frame in which there are five points of contact or more than five
points of contact, suitably placed to prevent sideways oscillations, and to permit
motion in the direction of the loops may be used. An ordinary slide may be used if
convenient.
When I wish the loops of the band to leave the sprocket wheels horizontally or
vertically or at any angle I use the apparatus shown in Fig. I Sheet 2 to constrain the
motion of the guide pulley frames. Each frame F, F, has five points of contact with
two of the group of 3 bars and each frame is maintained in contact with the bars by
springs and pieces similar to S, and P shown on Figs. 3 and 4 Sheet I.
The guide pullies G, G, are constrained to follow the motion of the loops and at
the same time to keep the steel band taut, by means of the spring S, acting on the
guide pulley frames by means of the cord C, C2 C3 C4 arranged as shown in Fig. I
Sheet 2. Fig. 2 Sheet 2 is a section at A B Fig. I Sheet 2.
Instead of the single spring S Fig. I Sheet II may use one or more springs
arranged to be lengthened or shortened by the relative angular displacement of the
two pieces to which they are connected and apply the sprocket wheels, endless band,
and measuring apparatus to measure the change in torque which produces the change
in form of the springs.
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed I declare that what I
claim is.
(1) The use of two pullies of equal diameter, or two sprocket wheels, or two
toothed wheels; of equal diameter operating on an endless chain or band placed over
them so as to form two loops so that a relative angular displacement of the sprocket
wheels, causes a relative linear displacement of the two loops; to measure the relative
angular displacement of the two pieces, pullies or shafts to which the before-
mentioned sprocket wheels are attached; by observing the change in the distance apart
of the two loops
or of any pullies or pieces placed in the loops and constrained to
follow their motion.
(2) The method of constraining the motion of the loops in one direction by means
of guide pullies mounted in frames guided by a group of bars, or a slide, and
constrained to follow the relative linear displacement of the loops by a spring or
springs substantially as described.
(3) The combination of a pulley mounted on ball bearings or any form of bearing,
and free to turn on the shaft but for its connection to the shaft by springs, and the
apparatus for measuring the relative angular displacement between the pulley and the
shaft substantially as described.
(4) The method of measuring the torque transmitted or existing between two
shafts, pullies or pieces substantially as described and shown in the drawings and
specification.
Dadth: ofth dox of Tahunance 1807
W. E. DALBY.