1. * GB780200 (A)
Description: GB780200 (A) ? 1957-07-31
Improvements in and relating to mechanical rotary motion coupling means
Description of GB780200 (A)
We, THE BRITISH THOMSON-HOUSTON
COMPANY LIMITED, a British Company, having its registered office at
Crown House, Aldwych, London, W.C.2, do hereby declare S the
invention, for which we pray that a patent may be granted to us, and
the method by which it is to be performed, to be particularly
described in and by the following
statement: -
This invention relates to mechanical coupling or transmission of
motion and aims at providing a means for deriving from a more or less
constant or continuously variable speed rotation a successively
retarded and accelerated rotational output movement which may serve
for a step-by-step drive.
Such drive is often required to change the position of a device in
discrete steps. For instance, the setting of certain aircraft
instruments requires adjustment in discrete steps according to the
changing altitude zones in which the aircraft is operating.
The present invention makes it possible to produce a step-by-step
rotation or angular position changes at predetermined intervals of a
continuous (as opposed to step-by-step) rotational input. Furthermore
the invention ensures operational stability by providing a
predetermined separation of the points at which the acceleration, that
is discrete changes of position, occur if the rotation of the input is
in one direction, from those associated with the other direction of
rotation, if such rotation must be expected in both directions.
Accordingly this invention resides in a rotary motion transmitting
device comprising driving and driven members rotating about a common
axis and interconnected by a resilient member arranged to be loaded
when the two members are angularly dis[Price 3s. 6d.] placed, a catch
supported by a stationary member being biased for movement into the
path of a stop of the driven member, and cams associated with the

2. driving member being provided to control the movement of the catch
into and out of the path of the stop, wherein the driving and driven
members comprise circular discs, and the resilient member comprises a
loop-shaped spring interconnecting tongues which project from the
discs at right angles thereto, and are radially aligned with each
other in their rest or neutral position.
In a preferred embodiment the catch is formed by a pawl riding on the
peripheral surface of the driving member and springbiased towards the
axis of rotation. A.
portion in the periphery of the driving disc is cut away so that the
pawl when it coincides with this recessed portion is allowed to move
towards the axis of rotation. The stop is formed by a second tongue
that is a projection on the driven disc, and on contacting this
projection the pawl arrests the motion of the driven disc for a
period, during which energy is stored in the coupling spring, until
the pawl is moved out of the recess of the driving disc by means of a
tapered end of the said recess. The coupling spring which has been
stressed by the relative angular movement between the two discs during
said period, then causes the driven disc to rotate at a higher speed
until it is again in phase with the driving disc and follow its
rotation at the slower normal speed of the input motion.
The driven disc may be connected through a shaft to an intermittent
movement, such as that used in a revolution counter, or any other
suitable mechanism which responds only to the higher speed of the disc
and disregards the intermediate low speed rota780,200 PATENT
SPECIFICATION
Inventor:-BERNARD ROY TUPPEN.
i&% Date of Jlli'ng Complete Specification: Aug. 11, 1955.
Application Date: Aug. 12, 1954. No. 23462/54.
/ CoCmplete Specification Published: July 31, 1957.
Index at Acceptance:-Class 80(2), 02F4D(3: 5).
International Classificationr:-Ee6d.
COMPLETE SPECIFICATION.
Improvements in and relating to Mec liicga RotRJY Motion Coupling
Means.
2 78( tion. The output of this movement. therefore, is a series of
discrete steps or rotation occurring at predetermined intervals while
the driving disc rotates miore or less uniformly.
Assuming that the input rotation is of constant speed, and that there
is only one peripheral recess, or that several such recesses are
equally spaced, then the steps must occur at equal time intervals.
These conditions are assumed only for illustration. The speed of the
driving disc need not be constant, and several recesses can be
differently spaced from one another along the periphery of the driving

3. disc.
As the projection which is engaged by the pawl has a finite width,
there will be an angular, and therefore a time, displacement between
the said steps corresponding to the two directions of rotation of the
driving disc.
This is a further feature of the invention, suitable tQ eliminate
points.of instability in operation when the input rotation is
reversed.
The width of the projection can be designed so as to afford a
separation of the operating points' corresponding to each direction of
rotation by a desired amount.
The invention will now be described more fully with reference to the
dlrawings accompanying the ProVisional Specification, in which:Fig. i
shows an end elevation; and Fig. 2 shows a side elevation of a
preferred embodiment.' A driving disc 1 mounted on an input shaft 2
has a peripheral recess 3. This disc carries a tongfie 4 which at its
rest or centre position coincides angularly witli a tongue carried by
a driven disc 6, the coincidence of ihe two tongues being resiliently
maintained by a pretensioned coupling spring 7 which engages both.
Also carried by the driven disc 6 is a second tongue 8, which normally
lies in the centre of recess 3 of the disc I.' 'Riding on the
periphery of the disc 1 is a pawl 9, which is biased towards the shaft
2, so that when it coincides with the cut away portion, that is the
recess 3 of the disc 1 it moves towards the centre of rotation. The
pawl extends laterally and on further rotation of the two discs it
engages the tongue 8, and arrests the motion of the driven 'disc 6
thereby loading the spring 7 until the pawl 9 is lifted by the
suitably shaped cam portion at the end of the recess to disengage the
tongue 8. The accumulated power of spring 7 then causes the driven
disc to accelerate and rotate rapidly until the tongues 4 and 5 are
re-aligned, whereupon the disc 6 rotates with disc 1, is arrested
again by the pawl 9, and so on in 12-00 repeated succession as long as
disc 1 rotates.
ThDiedriidi'sc 6 is connected by means of a shaft 10 to an
intermittent movement 11 of any type known in the art, the output of
which comprises step-by-step rotational displacements synchronised
with the occurrences of the high speed displacement of the driven disc
6.
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