Improvements in Apparatus and Devices for Starting, Stopping, and Reversing Electro Motors.
Year: 1893

page_text: Date of Application, 8th Aug., 1893-Accepted, 9th Sent., 1893
COMPLETE SPECIFICATION.
Improvements in Apparatus and Devices for Starting, Stopping, and
Reversing Electro Motors.
I, FRANK ALVORD PERRET of 43 Montgomery Place, in the City of Brooklyn,
County of Kings, State of New York, United States of America, Electrical
Engineer, 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 :-
This invention relates chiefly to that class of elevators in which a platform or
car is caused to ascend or descend by means of cables attached thereto, which pass
over a pulley or drum at the top of the shaft and thence around a winding drum,
which may be located on any floor.
Such elevators may be divided into two classes: (1) those in which the speed of
hoisting or lowering may be varied at will by the operator in the car. This feature
is essential in high speed passenger elevators as it is necessary to slow down just
before reaching a landing in order to make an accurate stop at the landing, and
(2) those elevators in which the speed of the car is practically constant in both
hoisting and lowering or is independent of the control of the operator on the car
who simply has the power to start the car either up or down and to stop same.
This invention relates to the latter class.
Until recently in nearly all elevators of this class the winding drums were driven
by belts from a constant source of power, the arrangement being such that when
the elevator is not in use the belt runs on a loose pulley. When the operator
desired to go up he pulled the rope passing through the car in one direction, which
shifts the belt to a tight pulley; pulling the rope back shifts it back to the loose
pulley and stops the car; pulling it in the opposite direction shifts another belt on
to the tight pulley which moves the car in the opposite direction.
Electric motors have been used in many cases as the sources of power and
connected thus by belts to the elevators, in which case the motor is usually allowed
to run constantly, which is wasteful of current, or the attendant has to go to a line
switch and shut off the current to stop it, which is inconvenient.
In order to avoid these objections, motors have been coupled direct to the
elevator machine and switching devices have been connected with the usual
operating cord by means of which the motor is stopped, started and reversed.
The invention herein described is concerned with the starting devices for the
electric motor, and, although the description refers to it in connection with an
electric elevator, it is well adapted as a motor starter wherever motors are used,
especially for railway motors.
In the accompanying drawing:
Fig. 1 represents a general view of the apparatus as applied to an elevator, and
Fig. 2 is a diagram of the circuits.
Referring to the drawing by letter, M is an electric motor which I prefer to be
shunt wound and which is connected to constant potential mains, LL. I have
shown the motor operatively connected to the winding drum R of an elevator by
a worm G, and a gear wheel G', but the invention is equally applicable to a spur
gear or to a belt connection. S is the brake, which is applied by means of the
weight W, which is adjustable on the lever N. This lever may be lifted and the
brake released in the old fashioned way by means of a mechanical device connected
with the sheave wheel E, around which the operating cable C passes, but I prefer
to lift the lever N and release the brake by means of an electro-magnet or
solenoid B, which is connected in the armature circuit or preferably in shunt as
shown in the diagram. As soon as the current is admitted to the coils of this

page_text: solenoid it sucks in its armature, raises the lever N, and releases the brake. The
instant the circuit is opened at any point, by any means, the solenoid is de-energized
and the weight W drops and applies the brake. F is a reversing switch, which is
powerfully actuated by a sheave wheel over which the operating cable passes. I
prefer that the movable portion of this switch should be mounted upon the sheave
wheel while the two sets of clips O and P, with which it makes contact, are
stationary. Fig. 1 shows this switch at its central position, at which point both
armature and field circuits are open. A pull on the cable in one direction closes
both field and armature circuits and causes rotation of the drum in one direction.
A pull on the cable in the other direction closes both field and armature circuits
and, as the armature circuit is reversed, produces rotation in the opposite direction.
Each set of the clips of this switch consists of six contact points, three being
arranged on each side of a block of insulating material, and there will be four
metallic blades pivoted to a block of insulating material / carried by the
sheave. Two of these blades are supposed to be directly behind the two shown in
Fig. 1. The two blades standing to the right are adapted to make contact with
the six clips O, one blade connecting three clips and the other blade the other
three clips. The same arrangement occurs on the left hand side.
H is a rheostat which is connected in the armature circuit. The diagram shows
the brush on the lowest contacts at which points all the resistance is in circuit, and
there should be sufficient resistance to protect the armature when at rest from a
current in excess of its safe carrying capacity. The contact brush of this rheostat
is attached to the armature of the solenoid A, which is connected in a direct shunt
to the brushes of the motor, the resistance H being outside of the terminals of the
shunt. Hence little or no current will flow through the solenoid until the armature
commences to turn and to generate a counter electro-motive force. Then the
current in the solenoid will increase in proportion to the increase of counter electro-
motive force generated by the armature and will not be affected in any way by the
condition of the rheostat. The solenoid therefore is controlled entirely and only
by the difference of potential between the positive and negative sides of the motor
armature.
We will now suppose the switch F to be open, as shown, and that the operator
pulls the cable to start the mechanism. This closes the switch F, and the circuit is
at once made through the field magnets and armature of the motor, the rheostat H,
its solenoid A, and the brake solenoid B. The circuits are traced as follows:
Referring to Fig. 2, the dotted lines indicate the two right hand blades thrown
into contact with the two groups O of three clips each. When the switch is in this
position the current is led from the positive line to clip 1, thence to clip 2, along
the switch blade to clip 3, thence by wire 4 through the armature of the motor,
wire 5, rheostat H, wire 6, clip 7, switch blade, clip 8, wire 9 to the negative main.
The field magnetic circuit branches at clip 3 and is led through the switch blade to
clip 10, thence by wire 11, wire 12, through the field magnet, wire 13, wire 14,
clip 15, and joins the armature circuit at clip 7. The brake solenoid B is connected
in wire 16 across the armature and outside of the rheostat H. The controlling
solenoid A is in circuit 17 directly across the brushes of the motor. The brake
solenoid instantly attracts the armature, raises the weight W, and releases the
brake. Unless there is an excessive load on the car the armature will commence at
once to revolve, will accelerate rapidly, the counter electro-motive force generated
by it will increase and the current through the solenoid A will increase corre-
spondingly, causing it to draw up its armature with increasing power, thereby
moving the contact brush across the row of contacts on the rheostat and cutting
out resistance step by step until it reaches the top where the resistance is all out
and the motor is running at full speed.
In case there should be an excessive load on the car or it is prevented from
moving freely, the current, which is at first admitted to the armature through the
rheostat, will not start the motor; consequently the solenoid A will receive
practically no current, and will not attract its armature with sufficient power to

page_text: move the contact brush on the rheostat. Consequently no resistance will be cut
out. The operator seeing that the motor does not start, will open his switch and
will hunt up the trouble, or if it is overloaded will ask somebody to step out.
The solenoid will work against gravity, preferably, so that the weight of its
armature will resist the small pull of the coil due to the little current which may
flow through it while the motor armature is stationary; or a spring may be used
to accomplish the same thing. A represents a dash pot or air cushion of any suitable
construction, used, if necessary, to prevent the too rapid movement of the solenoid
armature.
We will now suppose the mechanism to have been put into operation as already
described, and that a stop is to be made. The operator pulls the cord until the
switch reaches the central point where a stop i will prevent its going further, until
the contact brush of the rheostat has dropped again to the bottom and all the
resistance is in circuit. This stop is held against the periphery of the switch wheel
while the motor is running, but when the wheel is moved to the middle position to
stop the motor it falls into the notch and locks the wheel until it is removed there-
from by the end of the resistance controlling arm when it reaches the point where
all the resistance is in circuit. This prevents reversing until the resistance is put
in. As soon as the circuit has been broken at the switch F, as just described, the
solenoid B is de-energized and the brake is applied.
It will be seen that this principle of controlling the starting of the motor by the
counter electro-motive force generated by the motor armature is applicable to
motors driving railway cars or any other apparatus and is a sure protection to the
motor.
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:
1. An electric motor having a main or armature circuit and a shunt or field
circuit, and a rheostat in the armature circuit, in combination with a third circuit
including an electro-responsive apparatus controlling the rheostat, said third circuit
being a direct shunt to the brushes of the motor, substantially as described.
"
2. The combination of an electric motor and its circuit, an electric switch
controlling said circuit, a locking device for said switch when in its "open"
position, a rheostat in the motor circuit and an electro-responsive apparatus
operating the rheostat and the said locking device, substantially as and for the
purpose set forth.
Dated this 5th day of August A.D. 1893.
WILLIAM E. HEYS,
Agent for the Applicant.