Improvements in Electrical "Damping" Apparatus.
Year: 1899

page_text: PROVISIONAL SPECIFICATION.
Improvements in Electrical "Damping" Apparatus.
I, GEORGE WILLIAM JOHNSON, of 47, Lincoln's Inn Fields, in the County of
London, Patent Agent, do hereby declare the nature of this invention (which
has been communicated to me from abroad by Hartmann & Braun, of Bocken-
heim, Frankfort-on-Maine, in the German Empire) to be as follows:-
This invention relates to an electrical eddy-current "damping" device com-
prising rotating metal bodies and brake-magnets moveable in relation to each
other.
It is desirable to provide for electrical "damping' an arrangement which
does not act in strict proportion to the motion to be damped," but may be
regulated within certain limits of its dependency upon such motion, or in other
words be made self-regulating. Such a varying damping arrangement might
for example be applied with advantage to electrical meters (or apparatus for
measuring electricity) constructed as motor-meters," as apparatus of this class,.
wherever the electrical damping is precisely proportioned to the speed (or
velocity), give inaccurate measurements as at the outset, the speed or velocity
is slow, owing to friction, while as they reach the extreme limit of their scope
of measurement their rotation also becomes too slow owing to the additional
resistance produced by the air and to the counter-electromotive forces which
assert themselves. This invention has for its object to effect electrical damping,
at a medium velocity, more powerfully than at a very low or very high degree
of velocity.
As is generally usual, a metal block or body is employed, which is moveable
relatively to permanent or electro-magnets; the arrangement being such, that,
where such metal body participates in the rotary motion, part of the magnets---
or where the magnets share in the rotary motion, the whole or part of the metal
body, are made not altogether stationary, but yielding. Now if, in the one
case, the metal body, or in the other, the magnet system, be set in rotary motion,
there come into existence eddy-currents having a damping action, which at the
same time set the parts which have been made yielding in motion, or cause them
to alter their position. Now if the arrangement should be such that, while this
change of position takes place, the desired change also occurs in the damping
effect, the object contemplated is attained.
A damping arrangement according to this invention may be provided in the
following manner.
A metal disc, fast on a shaft or spindle, revolves between the poles of two
magnets, one of which is stationary, and the other capable of oscillating on
pivots, it being maintained in a predetermined position by a spiral spring or its
equivalent.
As the spindle together with the disc revolves eddy-currents are generated in
the disc by the magnets; which currents have a tendency to check the motion,
this checking being the only effect in so far as the stationary magnet is con-
cerned. As regards the oscillatory magnet the eddy-currents also produce a

page_text: tendency to move it in the direction of rotation of the disc, with the result that
this magnet performs a partial rotary movement, the angle of its displacement
being greater, the higher the speed of the disc. The damping effect at the same
time subsists, but its magnitude is no longer the same as in the case of the
stationary magnet as the point of influence of the damping forces varies with the
speed, such point, with increasing velocity moving farther and farther away
from the spindle, so that the damping effect rises more rapidly than the velocity,
until the magnet with its poles arrives near the edge of the disc, when the damp-
ing effect will begin to decrease.
This arrangement provides an eddy-current damping at low and high velocities
which is relatively less powerful than at medium velocities. The damping effect
may be rendered still more variable or modified by giving to various parts of
the revolving metal disc various degrees of thickness, or by increasing the resist-
ance of the same at certain points by providing notches therein. The moveable
magnet may be fitted with an index hand or pointer to indicate on a scale either
the existing velocity direct or the number of watts or amperes corresponding
thereto.
101
2
JOHNSONS & WILLCOX,
47, Lincoln's Inn Fields, London, W.C., Agents.
. Improvements in Electrical "Damping". Apparatus.
A, GEORGE WILLIAM JOHNSON, of 47, Lincoln's Inn Fields, in the County of
London, Patent Agent, do hereby declare the nature of this invention (which
has been communicated to me from abroad by Hartmann & Braun, of Bocken-
heim, Frankfort-on-Maine, in the German Empire.) and in what manner the
same is to be performed to be particularly described and ascertained in and by
the following statement:-
This invention relates to an electrical eddy-current damping device com-
prising rotating metal bodies and brake-magnets moveable in relation to each
other.
"
It is desirable to provide for electrical damping" an arrangement which
does not act in strict proportion to the motion to be damped," but may be
regulated within certain limits of its dependency upon such motion, or in other
words be made self-regulating. Such a varying damping arrangement might
for example be applied with advantage to electrical meters (or apparatus for
measuring electricity) constructed as motor-meters," as apparatus of this class,
wherever the electrical damping is precisely proportioned to the speed (or
velocity), give inaccurate measurements as, at the outset, the speed or velocity
is slow, owing to friction, while as they reach the extreme limit of their scope
of measurement their rotation also becomes too slow owing to the additional
resistance produced by the air and to the counter-electromotive forces which
assert themselves. This invention has for its object to effect electrical damping
at a medium velocity, more powerfully than at a very low or very high degree
of velocity.
As hitherto, a metal block or body is employed which is movable relatively
to permanent or electro-magnets, the arrangement being such, that, where such
metal body participates in the rotary motion, part of the magnets, or where the
magnets share in the rotary motion, the whole or part of the metal body, are

page_text: not altogether stationary, but are capable of yielding. Now if, in the one case,
the metal body, or, in the other, the magnet system, be set in motion, eddy-
currents are produced having a damping action, which at the same time set in
motion the parts which are capable of yielding or cause them to alter their
position. Now if the arrangement should be such that, while this change of
position takes place, the desired change also occurs in the damping effect, the
object contemplated is attained.
Figure 1 of the accompanying drawings represents in elevation an arrange-
ment of mechanism according to this invention and Figure 2 is a plan of a
portion thereof. C is a metal disc fast on a shaft or spindle A pivotted in a
frame B the said disc being arranged to rotate between the poles of magnets M² M².
The magnet M is stationary whilst the magnet M2 is capable of oscillating on
pivots, it being maintained in a predetermined position by a spiral spring f
unless acted upon by forces which happen to be in operation. By the rotation
of the spindle A together with the disc C eddy-currents are generated in the.
disc by the magnets MM², which currents have a tendency to check the motion
of the disc, this checking effect being the only result in so far as the stationary
magnet is concerned. As regards the magnet M2, which is movable, the
eddy-currents also produce a tendency to move the poles thereof in the direction
of rotation of the disc, with the result that this magnet performs a partial rotary
movement, the angle of its displacement being greater as the speed of rotation
of the disc C increases. The damping effect at the same time subsists, but its
magnitude is no longer the same as in the case of the stationary magnet M' as
the point of influence of the damping forces varies with the speed of rotation of
the disc C the said point of influence moving farther away from the spindle, so
that the damping effect rises more rapidly than the velocity, until the magnet M³
with its poles arrives near the edge of the disc, when the damping effect will
begin to decrease.
This arrangement provides an eddy-current damping at low and high velocities
which is relatively less powerful than at medium velocities. The damping effect
may be rendered still more variable, or modified by giving to various parts of
the revolving metal disc various degrees of thickness, or by increasing the resist-
ance of the same at certain points, for instance, by providing notches or open-
ings therein as shown in Figure 2. The movable magnet M₂ may be fitted with
an index hand or pointer Z to. indicate on a scale either the existing velocity
direct or the number of watts or amperes corresponding thereto.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed I declare that what I
claim is:
1. Producing electrical eddy-current damping by means of metal bodies in
magnetic fields the metal bodies and magnetic fields being movable relatively
to each other either the metal bodies or the magnetic fields being wholly or only
partly yielding, so that they alter their position with reference to each other
according to the speed or velocity of the movement of the damping parts of the
apparatus, and thereby vary the magnitude or degree of the damping force sub-
stantially as herein before described.
2. In apparatus for producing electrical eddy-current damping_the_combina--
tion of a metal disc arranged to rotate-in-a-field-of-permanent magnets, all or
part of which is revolvable or capable of yielding about an axis, the movement
of the magnet or magnets in the direction of rotation of the said disc being
caused by eddy-currents generated by the magnets in the revolving disc, the
distance between the magnetic field and the axis of rotation of the disc varying
with the velocity of the rotating disc, means such for example as a spring for
restraining the movement of the yielding magnets or magnet and for restoring
them or it after movement to the position of rest, slots or notches in the metal
disc, or parts of the disc being made thinner than other parts so as to produce a

page_text: variable resistance, and an index hand or pointer connected with one of the
yielding magnets to indicate on a scale the velocity, or the magnitude of the
forces causing the velocity, substantially as herein before described.
1000
JOHNSONS & WILLCOX,
47, Lincoln's Inn Fields, London, W.C., Agents.