By MARCEL DEPREZ.
[Footnote: _La Lumiére Electrique_.]
In a lecture delivered by me on the 15th of last June in the
amphitheater of the Conservatoire des Arts et Metiers, on the
application of electricity to the production, transmission, and division
of power, I operated for the first time an electric power hammer that I
shall here describe. Its essential part is a sectional solenoid that
I have likewise made an application of in an electric motor which I
presented in July, 1830, to the Societé de Physique. Let us suppose we
superpose, one on the other, a hundred flat bobbins of a centimeter
in thickness in such a way as to form a single solenoid one meter in
height, and that the incoming and outgoing wires of each of them be
connected with the contiguous bobbins exactly in the same way as they
are in the consecutive sections or a dynamo-electric machine ring.
Finally, let us complete the resemblance by causing each junction of the
wire of one of the bobbins with the wire of its neighbor to end in a
metallic plate set into an insulating piece containing as many plates as
there are bobbins, plus one. Over this species of collector, which maybe
rectilinear or wound around a cylinder, let us pass two brushes fixed to
an insulating piece that may be moved by hand. Now, if we place these
two brushes at a distance such that the number of the plates of the
collector included between them be, for example, equal to ten, and we
give them any degree of displacement whatever, after rendering them
interdependent, the current entering through one of these brushes and
making its exit through the other will always traverse 10 bobbins.
Everything will occur, then, as if we caused the ten-bobbin solenoid to
move instead of the brushes. This granted, and the brushes being in any
position whatever, let us send a current into the apparatus, and place
therein a soft iron cylinder. By virtue of a well known law, such
cylinder will remain suspended in the interior of the solenoid, and its
longitudinal center will place itself at so much the greater distance
from that of the solenoid the more the current increases in intensity.
It would even fall entirely if the current had not an intensity above a
minimum value dependent upon many elements concerning which we have not
now to occupy ourselves. We will suppose the current intense enough to
keep the distance of the two centers much below that which would bring
about a fall of the cylinder. When such a condition is fulfilled, it is
found that if we try to remove the iron cylinder from the equilibrium
that it is in, we must apply a pressure that increases with the amount
of separation, just exactly as if it were suspended from a spring. It
results from this fact that if we displace the brushes a distance equal
to the thickness of one plate of the collector, the active solenoid will
undergo the same displacement, and its longitudinal center will move
away from that of the iron cylinder, and that the attraction exerted
upon the latter will increase. It will not be able to assume its first
value, and equilibrium cannot be re-established unless the cylinder
undergoes a displacement identical with that of the solenoid. Now,
as this latter depends upon the motion communicated to the system
of brushes, we see that, definitively, the cylinder will faithfully
reproduce the motion communicated to the brushes by the hand of
the operator. This apparatus, then, constitutes a genuine electric
servo-motor in which the current is never interrupted nor modified in
quantity or direction, no more indeed than the magnetization developed
in the soft iron cylinder. Everything takes place as if the iron
cylinder were suspended in a solenoid ten centimeters in length that
was caused to rise and fall; with the difference that the weight of the
cylinder exerts no action on the hand of the operator.
[Illustration: ELECTRIC POWER HAMMER.]
These explanations being understood, there remain but few things to be
said to cause the operation of the hammer to be thoroughly comprehended.
The elementary sections constituting the electric cylinder, A B, of the
hammer are 80 in number, and form a total length of one meter. Their
ingoing and outcoming wires end in a collector of circular form shown at
F G. The brushes are replaced by two strips, C E and C D, fixed to the
double winch, H C I, which is movable around the fixed center, C. They
can make any angle whatever with each other, so that by trial there
maybe given the active solenoid the most suitable length. When such
angle has been determined, the angle, E C D, is rendered invariable by
means of a set screw, and the apparatus is maneuvered by imparting to
the double winch, H C I, an alternating circular motion.
The iron cylinder weighs 23 kilogrammes; but, when the current has an
intensity of 43 amperes and traverses 15 sections, the stress developed
may reach 70 kilogrammes; that is to say, three times the weight of the
hammer. So this latter obeys with absolute docility the motions of the
operator's hands, as those who were present at the lecture were enabled
to see.
I will incidentally add that this power hammer was placed on a circuit
derived from one that served likewise to supply three Hefner-Alteneck
machines (Siemens D{5} model) and a Gramme machine (Breguet model P.L.).
Each of these machines was making 1,500 revolutions per minute and
developing 25 kilogrammeters per second, measured by means of a
Carpentier brake. All these apparatus were operating with absolute
independence, and had for generator the double excitation machine that
figured at the Exhibition of Electricity.
In an experiment made since then, I have succeeded in developing in each
of these four machines 50 kilogrammeters per second, whatever was the
number of those that were running; and I found it possible to add the
hammer on a derived circuit without notably affecting the operation of
the receivers.
It results from this that with my system of double excitation machine I
have been enabled to easily run with absolute independence six machines,
each giving a two-third horse-power. The economic performance, e/E,
moreover, slightly exceeded 0.50.
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