IMPROVED APPARATUS FOR REGULATING AND GOVERNING THE SPEED OF ENGINES OR MACHINERY
Year: 1874

page_text: LETTERS PATENT to Alexander Melville Clark, of 53, Chancery Lane,
in the County of Middlesex, Patent Agent, for the Invention of
"IMPROVED APPARATUS FOR REGULATING AND GOVERNING THE SPEED OF
ENGINES OR
MACHINERY" -A communication from abroad by Farcot
Sealed the 24th November 1874, and dated the 3rd June 1874.
PROVISIONAL SPECIFICATION left by the said Alexander Melville
Clark at the Office of the Commissioners of Patents, with his
Petition, on the 3rd June 1874.
I, ALEXANDER MELVILLE CLARK, of 53, Chancery Lane, in the
County of Middlesex, Patent Agent, do hereby declare the nature of
the said Invention for "IMPROVED APPARATUS FOR REGULATING AND GOVERNING
THE SPEED OF ENGINES OR MACHINERY," to be as follows :-
-
This Invention relates to improvements in controlling or governing
steam and other engines used for working ships' rudders, capstans,
winches, hoists, cranes, and for other purposes.
[Price 8d.1

page_text: By means of the improvements of this Invention these engines are so
brought under control that they have received from the Inventors the
name of servo-motors, being based on the following distinct and essential
characteristics, namely, the subordination of the engine or motor to the
complete and absolute control of an attendant by making the hand of
the latter to move either directly or through a suitable medium with
the part to which the power of the engine or motor is applied, so that
the two move together, stop and reverse their motion together, the
engine or motor following step by step the hand of the attendant and
imitating its every movement, hence the name of servo-motor.
The Invention consists, 1st, in a new arrangement of the said servo-
motors having continuous rotary motion, and in which a variable lead
and partial expansion are obtained by means of a shifting or adjustable
eccentric turning loose upon a crank axis, the centre of the eccentric
itself moving in the arc of a circle passing through the axis of the main
or crank shaft.
The arrangement which I will now proceed to describe is illustrated
in Figures 1, 2, 3, 4, and 5, of the accompanying Drawings, in which
a, a', are steam cylinders. Any other gazeous liquid or liquid may
however be used instead of steam. These cylinders are inclined towards
each other at an angle of 90 degrees. b, b', are their pistons, and c, c¹, the
piston rods; d, d', connecting rods; e, e¹, piston rod guides; f, crank
shaft; g, g', valve chests containing the slide valves h, h¹; i, i¹, valve
rods connected to an adjustable eccentric n. This eccentric is caused to
oscillate by the action of the controlling gear hereafter described about
a geometrical axis S, S, which is quite distinct from the axis of rotation
of the crank shaft f, and is at such a radius therefrom that the eccentric
may be so adjusted relatively to the crank k as to give any required
grade of lead variable in either direction. This action is illustrated more
particularly in the diagram Figure 5, in which it will be seen that said
eccentric when at the middle of its angular movement is concentric
with the axis of rotation of the crank shaft f. It will thus be seen that
by such an angular movement or adjustment of the eccentric the throw
of the eccentric and consequently the travel of the slide valves will be
rendered greater or less, diminishing when the engine is working in onc
direction until it becomes nil, and then increasing when the engine is
reversed. Therefore to govern and keep the engine completely under
control it is merely necessary that the eccentric should be automatically

page_text: manoeuvred by the hand of the attandant, according to the method
indicated at the commencement of this Specification, and which may
be effected in various ways.
Figure 1 to 5 show one simple method of attaining this result:
j, screw thread cut near the end or at any other convenient part of
crank shaft f. A nut / toothed or not on its periphery is fitted on this
screw, and is operated or adjusted in a more or less direct manner by
the attendant. Now any relative motion of the nut consequent on any
difference of speed between shaft f and nut / causes the latter to traverse
along the former in a longitudinal direction. A sleeve m also mounted
on shaft is caused to turn therewith by a key m¹ moving in a longi-
tudinal keyway in the shaft, which permits of the sleeve being moved
along in either direction by the nut 1, which is coupled thereto by a
collar or other means, represented by m", admitting of the one part
rotating freely in the other.
The sleeve m, which may moreover be operated in many other ways,
according to circumstances, is formed exteriorly with one or more
spirally inclined surfaces, which by the longitudinal traverse of the
sleeve through a socket n' forming part of the eccentric n causes the
latter to perform a partial rotation in one or other direction on its
axis S, S, whereby the eccentric is adjusted in a gradual or progressive
manner so as gradually to increase or diminish the travel of the slide
valve h, h¹, to accelerate or reduce the speed of the engine as required,
the lead varying, that is to say, increasing or diminishing in the same
ratio. The lead is therefore reduced to nil as the motion of the valve
ceases when shifting the eccentric from the position of forward to that
of backward gear the throw of the eccentric, and consequently the travel
of the valve becoming reduced to nil at this moment, since the arc in
which the centre of the eccentric moves when turning loosely on its
axis S, S, passes through the centre of rotation of main shaft f. This is
a characteristic feature of the Invention. Such an arrangement of servo-
motor possesses great advantages as regards economy of steam owing
more especially to the lead both for admission and eduction and to the
partial expansion which is rendered possible, while at same time
retaining the greatest precision and facility in reversing, at which
moment, as before mentioned, the valve has no lead. This method of
distribution thus presents exceptional advantages, which are obtained
with the utmost simplicity of construction. The system of controlling

page_text: gear may be thus said to consist in governing the motor by the employ-
ment of an adjustable eccentric whose true centre moves in the arc of a
circle passing through the centre of rotation of the crank shaft, and
which thus under the governing action of the controlling gear gives a
course progressively variable together with a lead, which also increases
or diminishes simultaneously with the travel of the slide valves. The
rotation of the shaft f is transmitted by a pinion p and cog wheel p", or
by other means to a shaft q, on which I have shown a spirally grooved
drum or windlass g" of variable radius. By means of this arrangement
the moment of the resistance may according to any pre-arranged rule
be varied so as to constantly equal as near as possible that of the
power.
In cases where the spiral drum would be in too close proximity to the
guide pulleys of the tackle it is preferable to make the windlass with a
double groove or with two parallel grooves winding concurrently round
the barrel, the said grooves or spirals being so formed as to preserve an
exact equality between the amount of tackle wound on and that un-
wound from the drum. This drum of variable radius is not only
applicable for manoeuvring ships' rudders, but may also be used for
other purposes. This drum might however be replaced by one of cylin-
drical form, as indicated in dotted lines in Figure 8, or any other suitable
mode of transmitting the motion may be employed.
Figures 6 and 7 show modifications of the same class of controlling
gear as applied to a steam windlass, composed of two vertical engines
working separate cranks r, r', fixed at right angles to one another on the
shaft f, which gears by an endless screw 711, 71, or other means with the
drum shaft V, V, VI, bearing brackets for the crank shaft, which also
serve as abutments, and are made adjustable by means of stirrup
pieces u, u', having inclined surfaces, as shown. The eccentrics n, n',
which govern the distribution are connected to the slide valve rods i, i¹,
and, as in the preceding arrangement, are made adjustable under the
action of the controlling gear about an axis S, S, which is distinct from
that of shaft f. This adjustment is, as in the former case, effected by
the introduction into sockets n, n', of sleeves m fitted to slide longi-
tudinally and without angular motion on shaft f. It will thus be seen
that the method of adjustment now applied to two eccentrics is the same
as that before described in reference to a single eccentric. The sleeves m
may be operated in various ways.

page_text: In the example shown two bevil pinions o, v, are employed, each con-
taining a nut v¹ screwed on shaft f, and made square or polygonal on the
exterior to fit in the socket of the pinion. The pinions thus rotate the
nuts v³, v¹, which are coupled at m" with sleeve m so as to turn inde-
pendently thereof, and thereby move the latter back or forth for
operating the eccentrics n, n. The bevel pinions ♥, v, are operated by a
bevil wheel " on the drum shaft o, or in other manner, the teeth
of the gearing being skewed to suit the relative positions of the
axes.
Figures 8 and 9 show another mode of operating the sleeves m, m,
for adjusting the eccentrics. In this case the sockets v', ',' are operated
by levers v, 1, which are actuated by nut y of the controlling gear
mounted on one of the shafts, the traverse of this nut producing the.
effect desired. The nut is traversed either by a hand wheel y' or by a
pitch chain through the medium of toothed wheel y".
Figures 10 and 11 show another modification, in which the adjustment
of the eccentrics n, n, is directly operated by means of lugs n', n', and
spur wheels v, v, the centres of oscillation of the eccentrics being at S, S,
as before, and distinct from the axis of rotation of shaft f. The radial
play of the lug n' in the fork n", and of the wheel by which it is
operated, compensates for the difference of curvature of the arcs
described from the axis s, s, f, f. The wheels v are operated by
wheels, 1, and fly wheel y, or by the pitch chain y".
All the above arrangements readily admit of variation, the essential
object being to obtain by an adjustment of the eccentric a rapid reversal
of the engine, an economy of steam, and a suitable lead varying with
the travel of the slide valves, and reduced to nil as the valve arrives at
the position of no motion, as before explained.
Figures 12 and 13 show another method in which the travel of the
slide valves contained in the chest g is increased or extended by means
of levers b, b', the motion being imparted from shaft f, which is
equivalent to giving a much greater throw to the eccentric stud n
operating both the rods i, i. This stud n is oscillated on an axis S by
means of a circular rack m operated by a piñion u, concentric with shaft ƒ,
by partly rotating which the whole engine is controlled. The pinion u is
operated by another pinion x forged on the same axis and driven by a.
wheel, which through a pinion is actuated by an endless screw y',

page_text: which also serves to maintain the whole of the parts against any thrust
of the slide valves. It should be observed that this frictional resistance
necessary for maintaining the controlling gear against the thrust of the
slide valves is obtained in the other arrangements described by the
inclined surfaces of the spirals or by other means in the case of the
modification shown in Figures 10 and 11.
It should also be observed that pinion u may be made as small as
possible in order to lessen the power to be applied by the attendant to
the controlling apparatus during the rotation of the driving shaft f.
This result cannot be obtained with pinions mounted directly on shaft ƒ,
whose minimum diameter may even in some cases be comparatively
large. The endless screw y' is operated either by means of hand wheel y,
or pitch chain y", or in other manner.
The economical advantages and facility of working before specified in
respect of the gear for shifting the eccentric are equally applicable to
the class of machine shown in Figures 12 and 13, having a toothed
sector and multiplying gear for working the slide valves.
In order to manoeuvre the controlling gear in the several modifi-
cations of servo-motors before described, small auxiliary servo-motors
may be employed of any suitable construction.
Figure 14 shows the method of employing windlasses or drums of
variable radius for manoeuvring rudders or other apparatus.
In a preceding paragraph it has been shown that it is possible to
greatly improve the working of servo-motors having continuous rotary
motion by the employment for working the tackle of the drums of
varying radius already alluded to. Figure 14 shows an example of this
kind disposed on board ship, which possesses important and novel features
of improvement. a, rudder head; b, tiller shown in its midship position;
c, drum of varying radius operated by the servo-motor; d, ordinary
barrel operated by hand; n, n, tackle passing over guide pulleys in the
ordinary manner. The tackle n, when the tiller is in the midship
position, would be wound equally on each barrel so that the crossing
point on each is at the middle of its length. The ends of the tackle,
which consists of two parts, are made fast at four points, viz., to the two
ends of the ordinary barrel d, and to the two ends of the barrel of variable
radius c. The parts being thus arranged it will be understood that on
turning barrel c in one direction the length of tackle unwound will be

page_text: always equal to that wound on, the crossing point of the two parts
moving longitudinally, that is to say, parallel to the axis of rotation in
the helical groove of the barrel. The barrel d remains stationary, and
The tiller b is thus caused to move in
serves as purchase for the tackle.
the direction, or to the side at which the tackle is shortened, the total
length of the whole system of tackle remaining constant, as before
mentioned.
In working by hand the barrel c would serve as purchase for the
barrel d, and the latter becoming the motor would act on the tackle and
tiller in the same manner as the barrel c when the latter acted as motor.
No dismounting of any part of the apparatus is thus requisite in order to
adapt it for steering by hand or by the servo-motor.
In certain cases and with certain classes of servo-motors it might be
advantageous to employ the Stephenson link motion for governing the
distribution of steam, as shown in Figure 15, which represents an appa-
ratus of this description. a, main shaft; b, crank pin; c, c¹, eccentrics
and straps for operating the link; c", c", eccentric rods; d, Stephenson
link; n, slide valve. The form of valve shown may however be replaced
by one of the ordinary D form, equilibrated or not. The link d is oper-
ated in the ordinary way for reversing the engine by means of levers and
connecting rods e, f, oscillating on an axis g.
To control the motor it suffices to operate levere by any suitable
means subject to the action at one and the same time both of the atten-
dant and the motor. h, screwed socket or nut fitted on a rotating screw
shaft i, which participates in the motion of the engine, and which in the
Figure is a prolongation of windlass shaft j. The nut his operated by the
attendant by means of hand wheel h', and by its motion along the shaft i
the nut actuates the lever e', and through it the lever e, connecting rod f,
and link d. The driving shaft a actuates shaft j by a worm wheel k,
which is connected or disconnected with shaft j by means of a clutch 7.
It will now be readily understood that the attendant acting on the
wheel h¹ manoeuvres link d, and starts the engine, and so controls or
governs it that it can only move at the same speed and in the same
direction therewith. In a word the servo-motor is controlled by the
operation of the aforesaid Stephenson link.
The cylinder m is inclined at an angle of 45° from the vertical plane,
passing through the axis of shaft a, and is coupled in the ordinary.

page_text: with a similar cylinder placed symmetrically on the other side of the
shaft, the two piston rods consequently inclining together at an angle of
90°. The link of the second cylinder is operated by means of a lever
and connecting rod actuated from shaft g, the wheel h¹ thus governing
the pair of engines by the link motions. These arrangements may
however be varied as desired.
In applying these servo-motors for starting and reversing heavy
engines, such as marine engines, the arrangement and construction of
the servo-motor will of course vary according to the special requirements
of each case, its function being however in all cases to replace the hand
of the attendant, and act with any power, precision, and rapidity
desired.
In servo-motors having continuous rotary motion, as in all others, the
motive power of the apparatus may be conveyed to the rudder or other
apparatus by other means than the tackle before described. For this
purpose hydraulic tubes are especially applicable, the power being con-
veyed by hydraulic pressure to any desired distance, and made to act on
pistons or other known and suitable apparatus for working ship's rudders
and other purposes.
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said Alexander Melville Clark in the Great Seal Patent
Office on the 2nd December 1874.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, ALEXANDER
MELVILLE CLARK, of 53, Chancery Lane, in the County of Middlesex,
Patent Agent, send greeting.
WHEREAS
Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Third day of June, in the year of our
Lord One thousand eight hundred and seventy-four, in the thirty-seventh
year of Her reign, did, for Herself, Her heirs and successors, give
and grant unto me, the said Alexander Melville Clark, Her special
licence that I, the said Alexander Melville Clark, my executors, admini-
strators, and assigns, or such others as I, the said Alexander Melville
Clark, my executors, administrators, and assigns, should at any time agree

page_text: $
with, and no others, from time to time and at all times thereafter
during the term therein expressed, should and lawfully might make,
use, exercise, and vend, within the United Kingdom of Great Britain
and Ireland, the Channel Islands, and Isle of Man, an Invention for
'IMPROVED APPARATUS FOR REGULATING AND GOVERNING THE SPEED OF ENGINES
OR MACHINERY," a communication to me from abroad by Farcot and
Sons and Emile Duclos and Company, of Paris, France, upon the con-
dition (amongst others) that I, the said Alexander Melville Clark, my
executors or administrators, by an instrument in writing under my,
or their, or one of their hands and seals, should particularly describe
and ascertain the nature of the said Invention, and in what manner
the same was to be performed, and cause the same to be filed in the
Great Seal Patent Office within six calendar months next and imme-
diately after the date of the said Letters Patent.
NOW KNOW YE, that I, the said Alexander Melville Clark, do hereby
declare the nature of the said Invention, and in what manner the same
is to be performed, to be particularly described and ascertained in and
by the following statement, reference being had to the three accom-
panying accompanying Sheets of Drawings, and to the letters and
figures marked thereon (that is to say):-
This Invention relates to improvements in controlling or governing
steam or other engines used for working ships' rudders, capstans,
winches, hoists, cranes, and for other purposes.
By means of the improvements of this Invention these engines are so
brought under control that they have received from the Inventors the
name of "servo-motors," being based on the three following distinct and
essential characteristics, namely, 1st. The employment of an arrange-
ment of self-regulating controlling gear, which may be applied to any
motor or engine, and which shall be of sufficient power to render this
motor or engine completely and absolutely subservient to the will of the
attendant. 2ndly. The construction for this purpose of an arrangement
of gear, at one part of which the attendant will direct or regulate the
working of the engine by performing by a movement of the hand an
extremely small and relatively hardly appreciable part of the work to be
performed by the engine, the whole being so arranged that when the
hand of the attendant stops the engine or motor will stop immediately
and without fail, being controlled by its own motive power, the engine.

page_text: or motor, whether it increases or slackens speed, stops, or reverses its
motion, following step by step and with the greatest precision the hand
of the attendant, whose every movement it servily follows. 3rdly. The
placing of the centre of the gear in such a way that all useful motion of
the crank or other organ operated may take place without interfering
with the slide or other distributing apparatus, the latter being only
governed by a relative or differential movement of the hand of the
attendant.
The above features may be briefly summed up as consisting in the
subordination of the engine or motor to the complete and absolute
control of an attendant, by making the hand of the latter to move
either directly or through a suitable medium with the part to which the
power of the engine or motor is applied. Hence the name of " servo-
motor."
The Invention consists, 1st, in a new arrangement of the said servo-
motors having continuous rotary motion, and in which a variable lead
and partial expansion are obtained by means of a shifting or adjustable
eccentric turning loose upon a crank axis, the centre of the eccentric
itself moving in the arc of a circle passing through the axis of the main
or crank shaft.
The arrangement which I will now proceed to describe is illustrated
in Figures 1, 2, 3, 4, and 5 of the accompanying Drawings, in which
a, a¹, are steam cylinders. Any other gazeous fluid or liquid may
however be used instead of steam. These cylinders are inclined towards
each other at an angle of 90 degrees; b, b', are their pistons, and c, c¹, the
piston rods; d, d', connecting rods; e; e¹, piston rod guides; f, crank
shaft; g, g', valve chests containing the slide valves h, h¹; i, i¹, valve
rods connected to an adjustable eccentric n. This eccentric is caused to
oscillate by the action of the controlling gear hereafter described about
a geometrical axis S, S, which is quite distinct from the axis of rotation
of the cam shaft f, and is at such a radius therefrom that the eccentric
may be so adjusted relatively to the crank as to give any required
grade of lead, variable in either direction. This action is illustrated more
particularly in the diagram Figure 5, in which it will be seen that said
eccentric when at the middle of its angular movement is concentric
with the axis of rotation of the crankshaft f. It will thus be seen that
by such an angular movement or adjustment of the eccentric the throw

page_text: of the eccentric, and consequently the travel of the slide valves, will be
rendered greater or less, diminishing when the engine is working in one
direction until it becomes nil, and then increasing when the engine is
reversed. Therefore to govern and keep the engine completely under
control it is merely necessary that the eccentric should be automatically
manoeuvred by the hand of the attendant according to the method
indicated at the commencement of this Specification, and which may
be effected in various ways.
Figures 1 to 5 show one simple method of attaining this result;
j, screw thread cut near the end or at any other convenient part of
crank shaft f. A nut 1, toothed or not on its periphery, is fitted on this
screw, and is operated or adjusted in a more or less direct manner by
the attendant. Now any relative motion of the nut consequent on any
difference of speed between shaft f and nut / causes the latter to traverse
along the former in a longitudinal direction. A sleeve m also mounted
on shaft is caused to turn therewith by a key m', moving in a longi-
tudinal keyway in the shaft, which permits of the sleeve being moved
along in either direction by the nut 1, which is coupled thereto by a
collar or other means, represented by m", admitting of the one part
rotating freely in the other.
The sleeve m, which may moreover be operated in many other ways
according to circumstances, is formed exteriorly with one oľ more
spirally inclined surfaces, which by the longitudinal traverse of the
sleeve through a socket n' forming part of the eccentric n causes the
latter to perform a partial rotation in one or other direction on its
axis S, S, whereby the eccentric is adjusted in a gradual or progressive
manner so as gradually to increase or diminish the travel of the slide
valve h, h, to accelerate or reduce the speed of the engine as required,
the lead varying, that is to say, increasing or diminishing in the same
ratio. The lead is therefore reduced to nil as the motion of the valve
ceases when shifting the eccentric from the position of forward to that
of backward gear, the throw of the eccentric, and consequently the travel
of the valve, becoming reduced to nil at this moment, since the arc in
which the centre of the eccentric moves when turning loosely on its
axis S, S, passes through the centre of rotation of main shaft f. This is
the characteristic feature of the Invention. Such an arrangement of
servo-motor" possesses great advantages as regards economy of steam,
owing more especially to the lead both at the admission and eduction

page_text: and to the partial expansion which is rendered possible, while at same
time retaining the greatest precision and facility in reversing, at which
moment, as before mentioned, the valve has no lead. This method of
distribution thus presents exceptional advantages, which are obtained
with the utmost simplicity of construction. The system of controlling
gear may be thus said to consist in governing the motor by the employ-
ment of an adjustable eccentric whose true centre moves in the arc of a
circle passing through the centre of rotation of the crank shaft, which
thus under the governing action of the controlling gear gives a course
progressively variable, together with a lead, which also increases or
diminishes simultaneously with the travel of the slide valves. The
rotation of the shaft is transmitted by a pinion p and cog wheel p" or
by other means to a shaft q, on which I have shown a spirally-grooved
drum or windlass q" of variable radius. By means of this arrangement
the moment of the resistance may according to any prearranged rule
be varied so as to constantly equal as near as possible that of the
power.
In cases where the spiral drum would be in too close proximity to
the guide pulleys of the tackle, it is preferable to make the windlass
with a double groove or with two parallel grooves, winding concurrently
round the barrel, the said grooves or spirals being so formed as to pre-
serve an exact equality between the amount of tackle wound on and
that unwound from the drum. This drum of variable radius is not
only applicable for manoeuvring ships' rudders, but may also be used
for other purposes. This drum might however be replaced by one of
cylindrical form, as indicated in dotted lines in Figure 2, or any other
suitable mode of transmitting the motion may be employed.
Figures 6 and 7 show modifications of the same class of controlling
gear as applied to a steam windlass composed of two vertical engines
working separate cranks v, v', fixed at right angles to one another on
the shaft f, which gears by an endless screw 71, 71, or other means
with the drum shaft V, VI, bearing brackets for the crank shaft, which
also serve as abutments, and are made adjustable by means of stirrup
pieces u', u', having inclined surfaces, as shown. The eccentrics n, n',
which govern the distribution, are connected to the slide valve rods i, i",
and, as in the preceding arrangement are made adjustable under the
action of the controlling gear about an axis S, S, which is distinct from
that of shaft f. This adjustment is, as in the former case, effected

page_text: by the introduction into sockets n, n¹, of sleeves m fitted to slide
longitudinally and without angular motion on shaft f. It will thus be
seen that the method of adjustment now applied to two eccentrics is
the same as that before described in reference to a single eccentric.
The sleeves m may be operated in various ways.
In the example shown two bevil pinions v, v, are employed, each
containing a nut v¹ screwed on shaft ƒ and made square or polygonal on
the exterior to fit in the socket of the pinion. The pinions thus rotate
the nuts v¹, v', which are coupled at m" with sleeve m, so as to turn
independently thereof, and thereby move the latter back or forth for
operating the eccentrics n, n. The bevel pinions v, v, are operated by
a bevel wheel " on the drum shaft vv, or in other manner, the teeth of
the gearing being skewed to suit the relative positions of the axes.
Figures 8 and 9 show another manner of operating the sleeves m, m,
for adjusting the eccentrics. In this case the sockets v, v', are
operated by levers vlll, lll, which are actuated by nut y of the con-
trolling gear mounted on one of the shafts, the traverse of this nut
producing the effect desired. The nut is traversed either by a hand
wheel y' or by a pitch chain, through the medium of toothed wheel y".
Figures 10 and 11 show another modification in which the adjustment
of the eccentrics n, n, is directly operated by means of lugs n', n¹,
and spur wheels v, v, the centres of oscillation of the. eccentrics being
ats, s, as before, and distinct from the axis of rotation of shaft f. The
radial play of the lug n¹ in the fork n², and of the wheel by which
it is operated compensates for the difference of curvature of the arcs
described from the axes s, s, f, f. The wheels are operated by
wheels,, and fly wheel y, or by the pitch chain y².
All the above arrangements readily admit of variation, the essential
object being to obtain by an adjustment of the eccentric a rapid
reversal of the engine, an economy of steam, and a suitable lead varying
with the travel of the slide valves and reduced to nil as the valve
arrives at the position of no motion, as before explained.
Figures 12 and 13 show another method, in which the travel of the
slide valves contained in the chest g is increased or extended by means
of levers b, b', the motion being imparted from shaft f, which is.
equivalent to giving a much greater throw to the eccentric stud n

page_text: operating both the rods i, i. This stud n is oscillated on an axis S by
means of a circular rack m operated by a pinion u concentric with
shaft f, by partly rotating which the whole engine is controlled. The
pinion n is operated by another pinion a forged on the same axis, and
driven by a wheel x which through a pinion a" is actuated by an
endless screw y', which also serves to maintain the whole of the parts
against any thrust of the slide valves. It should be observed that this
frictional resistance necessary for maintaining the controlling gear
against the thrust of the slide valves is obtained in the other arrange-
ments described by the inclined surfaces of the spirals, or by other
means in the modification shown in Figures 10 and 11.
It should also be observed that pinion u may be made as small as
possible, in order to lessen the power to be applied by the attendant to
the controlling apparatus during the rotation of the driving shaft ƒ.
This result cannot be obtained with pinions mounted directly on shaft ƒ,
whose minimum diameter may even in some cases be comparatively
large. The endless screw y¹ is operated either by means of hand wheel y
or pitch chain y", or in other manner.
The economical advantages and facility of working before specified in
respect of the gear for shifting the eccentric are equally applicable to
the class of machine shown in Figures 12 and 13, having a toothed
sector and multiplying gear for working the slide valves.
In order to manœuvre the controlling gear in the several modifications
of servo-motors before described, small auxiliary servo-motors may be
employed of any suitable construction.
Figure 14 shows the method of employing windlasses or drums of
variable radius for manoeuvring rudders or other apparatus.
In a preceding paragraph it has been shown that it is possible to
greatly improve the working of servo-motors having continuous
rotary motion by the employment for working the tackle of the drums
of varying radius already alluded to. Figure 14 shows an example of
this kind disposed on board ship, which possesses important and novel
features of improvement. a, rudder head; b, tiller shown in its
midship position; c, drum of varying radius operated by the servo-
motor; d, ordinary barrel operated by hand; n, n, tackle passing over
guide pulleys in the ordinary manner. The tackle n when the tiller is
in the midship position would be wound equally on each barrel, so that

page_text: the crossing point on each is at the middle of its length. The ends of
the tackle, which consists of two parts, are made fast at four points,
viz., to the two ends of the ordinary barrel d, and to the two ends of the.
barrel of variable radius c. The parts being thus arranged it will be
understood that on turning barrel c in one direction the length of tackle
unwound will be always equal to that wound on, the crossing point of
the two parts moving longitudinally, that is to say, parallel to the axis
of rotation in the helical groove of the barrel. The barrel d remains
stationary, and serves as purchase for the tackle. The tiller b is thus
caused to move in the direction or to the side at which the tackle is
shortened, the total length of the whole system of tackle remaining
constant as before mentioned.
In working by hand the barrel c would serve as purchase for the
barrel d, and the latter becoming the motor would act on the tackle and
the tiller in the same manner as the barrel c when the latter acted as
motor. No dismounting of any part of the apparatus is thus requisite
in order to adapt it for steering by hand or by the servo-motor.
In certain cases and with certain classes of servo-motors it might be
advantageous to employ the Stephenson link motion for governing the
distribution of steam, as shewn in Figure 15, which represents an
apparatus of this description. a, main shaft; b, crank pin; c, c¹,
eccentrics and straps for operating the link; c", c, eccentric rods;
d, Stephenson link; n, slide valve. The form of valve shown may
however be replaced by one of the ordinary D form, equilibrated or not.
The link d is operated in the ordinary way for reversing the engine by
means of levers and connecting rods e, f, oscillating on an axis g.
To control the motor it suffices to operate lever e by any suitable
means subject to the action at one and the same time both of the
attendant and the motor; h, screwed socket or nut fitted in a rotating
screw shaft i which participates in the motion of the engine, and which
in the Figure is a prolongation of windlass shaft j. The nut his operated
by the attendant by means of hand wheel h', and by its motion along
the shaft i the nut actuates the lever e', and through it the lever e..con-
necting rod f, and link d. The driving shaft a actuates, shaft j by a
worm wheel, which is connected or disconnected with shaft j' by means
of a clutch 1.

page_text: It will now be readily understood that the attendant acting on the
wheel h¹ manoeuvres link d and starts the engine, and so controls or
governs it that it can only move at the same speed and in the same
direction therewith, in a word the "servo-motor" is controlled by the
operation of the aforesaid Stephenson link.
The cylinder m is inclined at an angle of 45° from the vertical plane
passing through the axis of shaft a, and is coupled in the ordinary way
with a similar cylinder placed symmetricalty on the other side of the
shaft, the two piston rods consequently inclining together at an angle of
90°. The link of the second cylinder is operated by means of a lever
and connecting rod actuated from shaft g, the wheel h' thus governing
the pair of engines by the link motions. These arrangements may
however be varied as desired.
Lastly. In applying these servo-motors for starting and reversing
heavy engines such as marine engines, the arrangement and construction
of the servo-motor will of course vary according to the special require-
ments of each case, its function being however in all cases to replace the.
hand of the attendant and act with any power, precision, and rapidity
desired.
In servo-motors having continuous rotary motion, as in all others, the
motive power of the apparatus may be conveyed to the rudder or other
apparatus by other means than the tackle before described. For this
purpose hydraulic tubes are especially applicable, the power being con-
veyed by hydraulic pressure to any desired distance, and made to act on
pistons or other known suitable apparatus for working ships' rudders
and other purposes.
'
Having described the nature of the Invention and the manner of
performing the same, I declare that what I claim as the Invention to le
protected by the herein-before in part recited Letters Patent is,-
First. The application to all kinds of engines or motors of a shifting
or adjustable eccentric or eccentrics turning loose upon a crank axis,
the centre of the eccentric itself moving in the arc of a circle passing
through the axis of the main or crank shaft, constituting a new or
improved system of continuous rotary servo-motor in which a variable
lead and partial expansion are obtained, substantially as shown and
described.

page_text: Secondly. The adjustment of the said eccentric or eccentrics either
first, by means of a large bevel whee " mounted on the shaft in motion,
gearing with two bevel pinions v, v, rotating nuts v³, v', which are
coupled with sleeves m and move the latter back and forth for operating
the eccentrics as shown in Figures 6 and 7, or secondly, by operating the
sleeve m by means of a nut y mounted on the rotating shaft and acting
through the medium of cranked levers,, as shown in Figures 8
and 9; or thirdly, by means of lugs n' engaging in forks n" of spur wheels
o receiving motion from the rotating shaft, substantially as described and
shown in Figures 10 and 11; or fourthly, by any other suitable arrange-
ment of controlling gear subjected to and operated by the hand of the
attendant, and the motion of the engine.
Thirdly. The arrangement of servo-motor having a toothed sector and
multiplying gear for extending the course of the slide valves, substan-
tially as described and shown in Figures 12 and 13.
Fourthly. The arrangement of continuous rotary servo-motor in which
the distribution of steam is governed by operating or shifting a
Stephenson link 'by controlling gear, as shown in Figures 12 and 13.
Fifthly. The application of these improved "servo-motors" for work-
ing ship's rudders and capstans, winches, hoists, cranes, and for other
purposes.
.5
Sixthly. The application to servo-motor windlasses" of drums of
variable radius, whereby the moment of the resistance may be varied
according to any pre-arranged rule so as to constantly equal as nearly as
possible that of the power as described and illustrated in Figure 7.
Seventhly. Working ship's rudders and other apparatus by the com-
bination of a drum of variable radius operated by a servo-motor, with an
ordinary hand barrel together with the special system of tackle, shown
in Figure 14, by which combination one or other of the said drums
may be operated without dismounting any part of the apparatus, the
drum not in use serving as a purchase for the one which is in work,
all as herein-before described.
Eighthly. The application of continuous rotary servo-motors for
starting and reversing heavy engines, generally and especially marine

page_text: Ninthly. Transmitting the motive power of continuous rotary servo-
motors as in all others to ship's rudders or other apparatus, through the
medium of hydraulic power or in other manner as described.
In witness whereof, I, the said Alexander Melville Clark, have
hereunto set my hand and seal, this Second day of December,
in the year of our Lord One thousand eight hundred and seventy-
four.
A. M. CLARK. (L.S.)