Improvements in Electric Hoists.
Year: 1896

page_text: Improvements in Electric Hoists.
I, WILLIAM HARDING SCOTT, of Gothic Works, Thorpe Hamlet, Norwich,
Norfolk, Electrical Engineer, do hereby declare the nature of this invention to be
as follows:-
The object of this invention is to arrange so that a series wound electric motor can
be made to work a hoist or elevator satisfactorily.
The speed of the motor is reduced on to the winding drum by means of worm gear
or other suitable means. A reversing switch is used operated by the stopping &
starting rope in the hoist. In hoists or elevators, for passenger or other purposes, it
is necessary that the hoist should stop quickly when the current is broken and it is
also desirable that the speed of going up and coming down, and also with the different
loads, should not vary very much. To get these results, I arrange, preferably on the
motor spindle, a brake wheel, and I apply to this brake wheel a brake operated by a
solenoid or electric magnet in such a way that when no current is flowing the brake
is on "hard" and the whole thing is stopped; but when a current of a certain
amount is flowing the brake is lifted off. On starting the motor a current of
considerable amount starts to flow, and the brake is lifted right off so that the motor
starts freely. If, however, the motor has very little to do the current in it will drop
and the speed of the motor would increase. To prevent this increase of speed being
too great, I arrange the solenoid or magnet in such a way that if the current in it
drops below a certain amount the brake is put partially on, and the current thus
prevented from falling below this amount. But this arrangement alone would involve
a considerable loss of efficiency when the hoist or elevator was coming down, in which
case the winding drum would have a tendency to drive the motor, so I arrange to
have an extra winding on the magnets which is put in circuit by the reversing switch
when this switch is operated for the coming down of the hoist. This extra winding
which is then in series with the ordinary winding, very much increases the number
of ampère turns on the magnets with a certain current flowing, consequently the
speed is reduced because of the greater excitation of the magnets with this current,
and I may also in this same circuit put in a resistance so as to reduce the power
operating the coming down of the hoist. By this means the amount of current that
the solenoid and brake arrangement must be adjusted to, in order to prevent the
hoist coming down too quickly, can be very much reduced and the efficiency very
greatly increased.
Dated this Fourteenth day of May 1896

page_text: Improvements in Electric Hoists.
I WILLIAM HARDING SCOTT Electrical Engineer of Gothic Works Norwich
Norfolk do hereby declare the nature of this invention and in what manner the
same is to be performed, to be particularly described and ascertained in and by the
following statement :-
The object of this invention is to arrange so that a series-wound electric-motor can
be made to work a hoist, lift or elevator in a satisfactory manner. The motor is
geared to the winding drum by means of a worm and worm-wheel or other gear
suitable for reducing the speed. In hoists, elevators or lifts for passenger or other
purposes it is necessary that the hoist should stop quickly when the current operating
it is cut off or interrupted from any cause, and it is also desirable that there should
not be any great difference between the speel going up and the speed coming down
with or without load. To obtain these results I arrange a brake wheel, preferably on
the motor spindle and I apply to this brake wheel a brake which is lifted or released
by a solenoid or electro-magnet in such a way that when there is no current flowing
the brake is "hard on" to the brake wheel and the hoist is stopped, but when a
current of a certain strength is flowing the brake is lifted off. On starting the motor
a considerable current flows and the brake is lifted right off immediately, so that it
does not resist the starting of the motor. If however the motor has very little load
on it the current will decrease and the speed of the motor will increase. To prevent
an excessive increase in speed I arrange the electro-magnet or solenoid which lifts the
brake in such a way that if the current falls below a certain amount the brake is put
partially "on" and the load on the motor being thus increased no further reduction
in the current can occur. But this arrangement alone would involve considerable
loss of efficiency when the hoist is descending or running in the direction which
involves the smallest load on the motor. In this case the winding drum might have a
tendency to drive the motor so that it might be possible to allow the hoist to descend
without supplying current to the motor if the brake were released by some other
means. But I do not consider that it would be desirable or safe to allow the hoist
to be free to move when current is cut off from the motor so in order to minimise the
loss of power or the current used when the hoist is descending I arrange to have an
extra winding on the motor magnets which is put in series with the ordinary series
winding of the motor by the act of putting the reversing switch in the position
required for lowering the hoist or for running in the direction in which least work
has to be done by the motor. This extra winding on the motor magnets very much
increases the number of turns and consequently reduces the current necessary for
their proper excitation, so that the solenoid or electro magnet may be adjusted to lift
or release the brake with a comparatively small current which will be sufficient, owing
to the extra winding on the motor magnets, to run the motor at a moderate speed and
thus prevent the too rapid descent of the hoist. By these means I use only a small
amount of electrical energy for lowering the hoist and at the same time retain all the
advantages of a series wound motor together with the safety due to my arrangement
for stopping the hoist immediately if for any reason the supply of electric current
should be cut off.
Referring to the drawing which shews diagrammatically the motor, brake, reversing
switch, cage and controlling rope but which does not show the gearing nor suspension
or hoisting ropes. A is the series wound motor, B B are the brake blocks on the brake
wheel B and C is the commutator of motor shewn diagrammatically with its
brushes. D is the solenoid the conductor on which is in series with the series
motor so that the brake is always on when no current flows through the motor

page_text: and is partially on when only a small current flows. E is the extra series coil
on the motor magnets, which is preferably of smaller conductor than the min
coils so that a larger number of turns or convolutions may be put into the space-
available. The reversing switch S is connected up as shewn in the diagram so
that if the controlling rope is made to operate it for raising the hoist or running
in the direction in which most work has to be done the brushes F and G bridge.
or connect the contacts H. M. and K. N. respectively and the extra series coil E.
on the motor magnets is not in the circuit, but when the controlling rope is
made to operate the reversing switch in the opposite direction, for lowering the
boist or running in the direction in which least work has to be done then this
extra series coil E is included in the circuit and consequently a smaller current
suffices to excite the motor magnets. The number of convolutions of conductor on
the brake solenoid and the proportions of the solenoid, or the equivalent electro
magnet, are so adjusted that the brake is lifted with the reduced current required to
sufficiently excite the motor magnets to prevent excessive speel or to keep the speel
within the limits allowable with the extra series coil E in circuit. If the current
tends to fall below this amount the solenoid no longer holds the brake clear of the
brake wheel so that the load on the motor is never allowed to fall below the minimum.
necessary to prevent excessive speed. It is clear that by the use of this extra series
coil on the motor magnets the minimum current necessary to prevent excessive speed
when lowering the hoist is very much reduced. For the purpose of providing a
convenient adjustment and of reducing the amount of work to be done on the brake
wheel I may include in the same circuit with the extra series coil E a resistance R
which can be adjusted to suit the conditions of each particular case and which is put
into and cut out of the circuit along with the extra series coil E.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed I declare that what I
claim is
The combination of a brake electrically released or lifted off the brake wheel or its
equivalent by the action of a coil or coils connected in series with a series wound electric
motor having an extra series coil or coils on its field magnets with a reversing switch
arranged so that the extra series coil or coils are excluded from the motor circuit
when the switch is in position for running the motor in the direction in which it has
most work to do, and the said extra coil or coils are included in the motor circuit
when the switch is in position for running the motor in the opposite direction.
Dated this Thirteenth day of February 1897.