IMPROVEMENTS IN TACHOMETERS OR APPARATUS FOR MEASURING THE VELOCITY OF ROTATORY SHAFTS
Year: 1877

page_text: LETTERS PATENT to John Henry Johnson, of 47, Lincoln's Inn Fields, in
the County of Middlesex, Gentleman, for the Invention of "IMPROVEMENTS
IN TACHOMETERS OR APPARATUS FOR MEASURING THE VELOCITY OF ROTATORY
SHAFTS." A communication from abroad by the Firm of Buss, Sombart, and
Company, of Magdeburg, in the Empire of Germany.
Sealed the 4th January 1878, and dated the 2nd November 1877.
PROVISIONAL SPECIFICATION left by the said John Henry Johnson at the
Office of the Commissioners of Patents on the 2nd November 1877.
JOHN HENRY JOHNSON, of 47, Lincoln's Inn Fields, in the County of Middlesex,
Gentleman. "IMPROVEMENTS IN TACHOMETERS OR APPARATUS FOR MEASURING
THE VELOCITY OF ROTATORY SHAFTS." A communication from abroad by the
Firm of Buss, Sombart, and Company, of Magdeburg, in the Empire of Germany.
This Invention relates to improvements in what are known as tachometers
employed for measuring the velocity of rotatory shafts, and it has for its object
enabling the number of revolutions to be read constantly by means of a hand and a
dial plate.
In carrying out this Invention the dial plate is graduated either with the
number of revolutions per minute, or with angular velocities, and the whole
instrument is so constructed as to render that division of a nearly perfect
uniformity.
According to one arrangement on the axis carrying the hand, which directly
indicates the velocities in numbers of revolutions, there is fixed a toothed wheel
which is in gear with a toothed segment. A small spiral spring is employed which
tends to turn the hand towards its initial position, thereby avoiding all inaccuracies
which might arise owing to the play of the teeth.
The axis of the toothed segment passes through the side of the case, and carries
a short lever on its outer extremity, which lever is connected by means of a con
necting rod to one arm of an angular or bell-crank lever capable of being turned

page_text: on its axis. As the said arm is considerably longer than the lever first mentioned
the angles of separation of the toothed segment are neither equal nor proportional
to the angles of separation of the angular lever, but in the end positions the degree
of motion imparted is greater than in the central positions. On the position of
equilibrium of the angular lever, which is provided with a weight and two friction
rollers, depends the position both of the toothed segment and of the hand.
The weight has a tendency to turn the angular lever in one direction, and a
vertical plate, which is arranged to press against the rollers, tends to move the lever
in an opposite direction. The plate is formed in one piece with a tube or sleeve, by
which it is guided in a rectilinear direction in a socket in the case, whereas a bar
screwed on to the plate becomes interposed between the rollers, thus obstructing the
turning of the plate.
In the interior of the case there is arranged mechanism somewhat resembling in
construction a centrifugal governor with the cast-iron.axis of rotation arranged in
a horizontal position. The piece which in this arrangement corresponds to the
governor sleeve or collar, consists of a cylindrical rod, which is guided both in a
hollow shaft and in the tube or sleeve before mentioned.
The hollow shaft carries a bowl with, say, four arms, & through each two
neighbouring arms pass respectively two pins which form the axes of two pendulums
of rotation. Each pendulum consists of a long sleeve, a half round disc, and a semi-
ring, on a lug formed on which is carried a pin. Each of these pins passes through
the head of a bolt, so as, whilst capable of being turned, to admit of the axial motion
of the bolt head. The bolts are fitted in sockets opposite to each other formed on
a cross piece attached to the sleeve shaft, the said bolts being capable of turning in"
their sockets, but not movable in an axial direction.
This apparatus transmits the motion of the pendulum to the sleeve rod in such a
manner that the latter in addition to its being moved in an axial direction at the
same time turns slightly towards the hollow shaft. This shaft, which itself turns
in a tube or sleeve, and forms the main axis, receives its motion from a small pulley
which is fitted over the said tube or sleeve, and thus transmits the lateral pressure
generated by the belt to such tube or sleeve, a screw pin or catch being employed for
connecting the pulley to the said hollow shaft or main axis..
The centrifugal force tends to turn both the rotary pendulums to the outside,
which thereby exert an axial pressure on the sleeve shaft, which pressure is trans-
mitted by the plate to the rollers of the angular lever. The greater therefore is the
angular velocity, and consequently the centrifugal force of the rotary pendulums,
the farther the angular lever is pressed outside, and the farther also the hand moves
on the dial plate.
It is preferred to employ for the purposes before mentioned rotary pendulums of
the description known as cosine pendulams, in respect of which Letters Patent were
granted to me, dated the 15th of April 1876, No. 1604, but other arrangements of
rotary pendulums may be substituted therefor. When cosine pendulums are
employed, the lever arm on which the centrifugal force works forms a right angle,
with the lever arm to which the sleeve shaft is attached.
In this case the pressure
exerted by the pendulums on the sleeve shaft depends on the angular velocity only,
but not on the position both of the pendulums and sleeve; it is on the contrary
for a given angular velocity fully uniform in all positions of the sleeve shaft.
According to another modification of the said Invention, which is chiefly intended
for locomotive and marine engines, the apparatus is arranged in the following
manner:- -The axis carrying the hand is in this case also furnished with a spiral
spring preventing the play of the teeth, and with a small toothed wheel or pinion.
The latter is however fastened eccentrically, and worked by a rack, bent or curved
to a suitable form. The ratio of transmission is therefore still, in both the end
positions of the hand, greater than in the central position, and that to such a
degree that a graduation of the dial plate is produced of a nearly perfect
uniformity.
For conducting the rack in a straight line two rods are employed, on which rods

page_text: the rack slides. To a lateral nose is attached the sleeve shaft consisting of a screw
with a multiple thread of a coarse pitch, of a long toothed pinion, and of two
cylindrical extremities, a cast-iron frame is provided having its bearings in sockets
in the case, and being operated by a pulley, which frame carries two steel pins
which are parallel with the main axis, and form the axes for the two pendulums of.
rotation. Each pendulum is provided in addition to its sleeve the pendulum arm
and a long cylindrical weight with a toothed segment, the said segments being in
gear with the long toothed pinion of the sleeve shaft. To each pendulum sleeve
there is fastened a broad steel spiral spring, which tends to move the pendulum
weight in the inward direction, that is to say, towards the main axis. Both spiral
springs are connected with each other by a ring. In the cast-iron frame a brass nut
is fixed, in which the screw before mentioned moves.
The centrifugal force has the tendency to move both the pendulum weights from
the main axis, and the tension of both the spiral springs tends to move them in an
opposite direction towards the said axis.
An alteration in the angular velocity of the main axis and of the centrifugal force
of the weights thus produces an alteration in the position of equilibrium of the
pendulums. Every motion of the pendulums by the two toothed segments is trans-
mitted to the long toothed pinion of the sleeve shaft, and the latter not only
receives. a relative rotation, but also a screw motion by reason of the arrangement
of the screw and nut. The axial motion of the sleeve shaft is then transmitted in
the manner described to the rack and to the axis carrying the hand.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said John Henry Johnson in the Great Seal Patent Office on the 2nd
May 1878.
་
JOHN HENRY JOHNSON, of 47, Lincoln's Inn Fields, in the County of Middlesex,
Gentleman. "IMPROVEMENTS IN TACHOMETERS OR APPARATUS FOR MEASURING
THE VELOCITY OF ROTATORY SHAFTS." A communication from abroad by Buss,
Sombart, and Company, of Magdeburg, in the Empire of Germany.
The said Invention relates to an improved "tachometer" or apparatus for
measuring the velocity of rotatory shafts, which admits of a continual and most
convenient reading of the number of revolutions indicated by a hand on a dial.
The apparatus is represented on the accompanying Drawings, constructed and
arranged according to three respective modifications.
Figures 1, 2, 3, 4, 5, and 6 (Sheet 1), and Figure 7 (Sheet 2) relate to the first
inodification, which is a tachometer intended for stationary rotatory machines of
every description, shafting, and the like.
Figures 8, 9, 10, and 11 (Sheet 3), represent the second modification, chiefly
intended for locomotives and marine engines.
Figures 12 and 13 (Sheet 3) représent the third modification, also intended
specially for locomotives and marine engines.
Referring to the first modification, which is illustrated by Figures 1 to 7 of the
Drawings; Figure 1 represents a vertical section through the whole apparatus ;
Figure 2 is a horizontal section of the same through the upper part; Figure 3 is
a horizontal section through the lower part; Figure 4 is a side view, partly in
section Figures 5 and 6 are details, which will be herein-after referred to; and
Figure 7 is a perspective view of the whole apparatus. The dial A is graduated
either with numbers of revolutions per minute or with angle velocities, and the
whole apparatus is so constructed that the division of the dial is almost of perfect
uniformity.
On the shaft B carrying the hand a, which indicates directly the velocities or
numbers of revolutions, there is mounted a spur wheel b, which is in gear with a
toothed segment C.. A small weak spiral spring c is employed which tends to turn
the hand towards its original position, thereby avoiding all inaccuracies which
might arise owing to the play of the teeth.
The shaft of the toothed segment C passes through the side of the case D, and
carries on its outer end a short lever d, which is connected by a rod E to the arm e
of a bent or bell-crank lever F, movable round the axis f. As the arm e is con-
siderably longer than the lever d, the angles of stroke of the segment C are neither
equal nor proportional to the angles of stroke of the lever F. Between the bell-
crank lever and the segment in both their end positions, as indicated by the dotted
lines, the degree of motion imparted is greater than in the intermediate positions.
The position of equilibrium of the bell-crank lever F, which is loaded with a
weight, and carries two similar friction rollers h, depends upon the position of the
segment C as well as upon that of the hand a.
Whilst the weight g tends to turn the lever F in one direction, a vertical plane
plate i tends to move the lever in the opposite direction by pressing against the
rollers h. The plate forms practically one piece with the long rod k, being guided
in a rectilinear direction by the latter, whilst a web (see Figure 7) screwed to
the plate is interposed between the rollers, thus preventing the turning of the
plate.
In the case H there is enclosed a mechanism which in construction greatly
resembles a centrifugal governor, with the difference that the cast-iron rotating
axis I is not placed vertically but horizontally. The piece which is the equivalent
to the collar or sleeve of the governor is the cylindrical tube K, shewn detached
in Figure 5, which is guided on the rod k, and by its projection m bears against
the plate i.

page_text: The hollow shaft I carries a bowl or concave appendage n, cast in one piece, with
four arms o, o, Figures 1 and 6, and through each two neighbouring arms in one
direction pass respectively two pins p (Figure 6), which form the axes of two
rotatory pendulums. Each pendulum consists (see Figures 1 and 5) of a long
rod q, a half disc r, and a half ring 8, the latter carrying a pin t. The two pins t
pass respectively through the oblong heads of the two bolts u, being movable therein
and admit of the axial motion of the bolt head. The two bolts are, placed in two
opposite axial perforations of the cross piece L (Figure 5), and are movable therein,
but not axially displaceable. The cross piece L is formed in one with or rigidly
secured to the sleeve K.
The mechanism above described transmits the pendulum motion to the sleeve,
so that the latter in addition to its axial motion receives at the same time a slight
longitudinal motion.
The mechanism for transmitting the motion of the pendulums to the sleeve may
be modified in various ways; for example, drawing rods may be employed which
connect the pendulums with the sleeve, or any other known equivalent mechanism
may be substituted therefor. The main shaft I, which turns in the socket M,
receives its motion through the intervention of a small pulley N which is placed
over the socket M, and thus transmits the side pressure produced by the belt to the
socket only and not to the shaft. The small screw w serves for transmitting the
motion of the pulley to the main shaft.
The centrifugal force tends to turn outwards the two rotarary pendulums, which
thereby exert an end pressure upon the sleeve K, which pressure is transmitted by
means of the plate i to the rollers of the lever F. The greater the centrifugal force
of the rotatory pendulums the farther is the lever F pressed outwards, and at the
same time the hand a is advanced on the dial.
It is preferred to employ for the purposes before mentioned rotatory pendulums
of the description known as cosine pendulums, in respect of which Letters Patent
were granted to me, dated the Fifteenth April One thousand eight hundred and
seventy-six, No. 1604, and so arranged that the lever arm on which the centrifugal
force acts forms a right angle with the lever arm with which the sleeve K is in
contact. In this case the pressure exerted by the pendulums ou the sleeve depends
only upon the angular velocity and not upon the position of pendulum and sleeve ;
this pressure of a determined angular velocity is equal in all positions of the sleeve,
and affords the following advantages:-
1. Any wear of the sleeve projection, or any variation in the size of which the
rollers h are constructed, has no influence upon the position of equilibrium of the
lever and the hand.
2. The lever possesses an extraordinary stability, that is to say, it requires for a
certain change of its position a much greater change of velocity than would be
required in employing any other rotatory pendulum. For moving the lever from
its lowest to its highest position (by employing the cosine pendulum) a quintupled
velocity is required.
If the motion transmitted from the lever F to the segment C were a uniform one,
the divisions on the dial, as a simple calculation might prove, would be smaller at
both sides than in the middle. This non-uniformity of division is almost completely
obviated by reason of the degree of motion imparted being greater in the end posi-
tions by means of the unequal levers. Although however the arrangement herein-
before described is preferred, any rotatory pendulum may be employed in which the
conditions of the cosine pendulum are approximately fulfilled.
Figure 8 (Sheet 3) is a transverse vertical section of an apparatus constructed
according to the second modification of the said Invention; Figure 9 is a longitu-
dinal vertical section; and Figure 10, a horizontal section of the same; Figure 11
shews in elevation and plan a pedulum detached.
In this arrangement, the dial, the shaft carrying the hand, the gearing, spiral
spring, and toothed segment are similar to those of the first modification. A short

page_text: P,
"
Two
drawing rod E connects the toothed segment with the rod k. This latter is situate
in a perforation of the rod k, which acts as the sleeve." The two similar pen-
dulums (Figure 11), consist of an equal armed rectilinear double lever, of the two
cylindrical weights 8, s', of the eye q, and the pin t. The two pendulums are sus-
pended crosswise, the one in proximity to the other, and are movable round the
common axis which is maintained fast by the fork-shaped support n.
drawing rods u and u' which resemble the drawing rods of the Watt governor,
form with the pendulum arms and an equilateral parallelogram, and connect the
pendulum with the "sleeve" K. Through each of the four pendulum weights passes
a pivot h or h¹ with which a small plate i is connected. Between each couple of
such plates is a spiral spring g arranged for compression. Both springs are placed
on the same side of the pendulum, and tend to remove the weights s and s¹
the one from the other, or press them towards the axial line of the apparatus.
A guide bar f connected by a disc 7 with the centre of the spring passes through
the axis of each spring, serving as a parallel guide to the plates. By means of a
weight m added to the pendulum support, or of another pair of springs arranged at
the opposite side of the pendulum weights, the other springs are released; thus any
shock upon the shaft is obviated.
All end pressures exercised by the springs and the centrifugal force are balanced
by this arrangement.
In order to render the position of the common centre of gravity constant, and
to prevent all liability of the correct position of the hands being influenced
either by an oblique position of the whole apparatus, or by shocks and concus-
sions, both weights 8, 8, are made smaller than the weights s¹, s¹, by an amount
which may be exactly determined by calculation.
Figure 12 (Sheet 3) is a vertical section of an apparatus constructed according to
the third modification of the said Invention; and Figure 13 is a horizontal section
of the same.
The whole mechanism enclosed in the case D is identical with that of the second
modification, with the exception only that the Drawing rod E supplied here by a
vertical pin d is fixed to k and to a bolt e with a perforated head. One half of each of
the two pendulums is dispensed with, so that the whole pendulum mechanism
resembles that of the Watt governor.
In lieu of the two springs of the apparatus last described, in this modification only
one spring g is employed, which presses the "sleeve" in one direction.
The essential difference between the pendulum mechanism employed in this modi-
fication and that of the Watt governor is, that by this construction the point of
junction, or the common axis p of both drawing rods u and u¹ is secured against
longitudinal displacement, and that the common axis z of the pendulums is movable
in the longitudinal direction. Moreover the pendulums are a little more than twice
the length of the drawing rods u and u', so that the pendulum weights perform
nearly radial movements and in the direction of the axis move only such a distance
as is required for maintaining the common centre of gravitation of the movable
parts.
It will be seen on reference to Figure 12 that the pendulum weights move longi-
tudinally in a direction the reverse of that of the motion of the "sleeve." The
lengths and weights of the pendulums are so calculated that the end movements of
the drawing rod, the spiral spring, the rod k, and the segment are also taken into
consideration, and the common centre of gravitation of the whole of the said parts
remains unchanged whatever may be the position of the pendulums, the "sleeve,"
and the hand. This tachometer, as well as that of the second modification, can
therefore be placed in a horizontal, vertical, or any oblique position, and may be
subjected to the shocks due to the pitching of a vessel, or be exposed to the violent
concussions of a locomotive without being moved from its position of equilibrium,
which depends only on the velocity, and without the liability of its accuracy being
impaired.

page_text: The parts shewn in Figures 8 to 11, and not specially referred to, are indicated by
the same letters as the corresponding parts in Figures 1 to 7, and similarly the
parts shewn in Figures 12 and 13, and not specially referred to, are denoted by the
same letters as the corresponding parts in the preceding Figures.
Having now described and particularly ascertained the nature of the said
Invention, and the manner in which the same is or may be used or carried into
effect, I would observe in conclusion that what I consider to be novel and original,
and therefore claim as the Invention secured to me by the herein-before in part
recited Letters Patent is,―
First. The arrangement of the lower part of the apparatus, consisting of a pen-
dulum mechanism placed horizontally, the "sleeve" of which exerts pressure against
a weighted lever, substantially as herein-before described, and illustrated by
Figures 1 to 7 of the Drawings.
Secondly. Employing in tachometers a transmission mechanism consisting of two
unequal levers d, e, and a drawing rod E for obtaining an approximately uniform
division, substantially as herein-before described, and illustrated by Figures 1 to 7
of the Drawings.
"
Thirdly. The so arranging the "sleeve" K and the rod k that the said "sleeve
can perform its motions only in the fixed part G, whilst the rod k which is non-
rotating can perform its end motions only in the rotating part I, so that the
frictional resistance of these motions is minimized, substantially as herein-before
described, and illustrated by Figures 1 to 7 of the Drawings.
Fourthly. The employment in tachometers of what is known as the cosine
pendulum in order to obtain a measurement of speed between limits as distant as
possible, and to adjust thereby the irregularities which occur with other pendulums
in consequence of the wear and tear of the sleeve, substantially as herein-before
described.
Fifthly. The general arrangement and combination of parts, substantially as
herein-before described, and illustrated by Figures 1 to 7 of the Drawings.
Sixthly. The general arrangement and combination of parts, substantially as
herein-before described, and illustrated by Figures 8 to 11 of the Drawings.
Seventhly. The general arrangement and combination of parts, substantially as
herein-before described, and illustrated by Figures 12 and 13 of the Drawings.
In witness whereof, I, the said John Henry Johnson, have to this my
Specification set my hand and seal, this Eighteenth day of April, One
thousand eight hundred and seventy-eight.
HRADY
TATTYCANY
J. HENRY JOHNSON. (L.S.)