US1245194A - Motor-control system. - Google Patents

Description

G. N. CRABBE.

MOTOR CONTROL SYSTEM.

APPLICATION FILED mm. 21. 1914.

1,245,194. Patented Nov. 6, 1917.

. M61 INVENTOR WITNESSES:

- UNITED STATES PATENT OFFICE.

GEORGE N. CRABIBE, OF CRESSKILL, NEW JERSEY, ASSIGNOR TO OTIS ELEVATOR COM- PANY, OF JERSEY CITY, NEW JERSEY, A CORPORATION OF NEW JERSEY.

MOTOR-CONTROL SYSTEM.

Specification of Letters Patent.

Patented Nov. 6, 191 '7.

Application filed March 21, 1914. Serial No. 826,144.

T '0 all whom it may concern:

Be it known that I, GEORGE N. CRABBE, a citizen of the vUnited States, residing in Cresskill, in the county of Bergen and State of New Jersey, have invented a new and useful Improvement in Motor-Control Systems, of which the following is a specification.

My invention relates to improvements in controlling systems for motors, and is adapted, among other things, automatically to prevent a too sudden reversal of an electric motor.

The invention is adapted to substantially all electric motors which are arranged to- 'have their direction of rotation reversed from time to time, but the same is particularly adapted to an electric elevator or hoist in which the motor is constantly being started, stopped and reversed under load.

I am aware that itis not new, broadly speaking, automatically to prevent a too su den reversal of the motor of an electric elevator or hoist but in general the method as used, is objectionable in that it results in a substantial loss of time.

For example, in a high rise electric elevator, such as one finds in the modern ofiice buildings of a large city, it is very essential that the elevator shall be'operated at high speed and with as little loss of time as possible in starting, stopping and reversing. In the present instance in particular, and in all other elevator installations to a lesser degree, an appreciable loss of time is occasioned in case the car operator centers his controlling switch to stop the car at a landing and then changes his mind before the car has had time to slow down and stop, and concludes to. continue in the same direction and immediately throws the controlling lever into the samerunning position that it was before he atte'mpted to stop. Under this condition, the

automatic means for preventing a too sudden reversal will prevent the operator from closing a circuit to the motor until after the latter has substantially come to rest, whereas it is entirely feasible to permit the operator a ain to close a circuit to the motor immediate y it has been opened, providing of course the motor circuit is closed in' the same direction as before and not in a reverse direction tending to effect a sudden reversal.

My invention provides a simple, practical and eflicient means for preventing a too sudbefore without having to wait until themotor has substantially come to rest or had its speed materially reduced, thereby effecting an appreciable saving of time, which, as above pointed out,'is most desirable. Figure 1 of the accompanying drawing is a diagrammatic representation of an electric elevator system containing an embodiment of my invention in a simple form; Fig. 2 is a detail view of an adjustable relay.

Referring to the drawing, an electric motor M is adapted to be started, stopped and reversed by means of the reversing switches R and R which are controlled by a switch S located in the elevator car or other convenient place. The reversing switches are preferably mechanically interlocking by means of a lever 10 having a pin and slot connection with each reversing switch, so

that it isimpossible for both switches simultaneously to be closed or in their extreme lowermost position. The motor field winding is represented by the letter F while an accelerating magnet A is arranged automatically to short circuit the starting resistance B in a plurality of steps in accordance with the load on the motor in a well known way. A pair of relays 20 and 30 have their windings connected in series across the motor armature and hence operate according to the varying counter-electro-motive force of the motor and consequently the speed of the motor. i

The operation of the controlling system is as follows: Assuming the parts of the apparatus in the position shown, the operator first moves the lever of switch S, say for exampleto the right, into electrical enagement with the contact 11. A circuit is now closed from the main, through the .magnet winding 12 of reversing switch R,

contacts 13 of relay 30, contact 11 of switch S and to the main. The core 14 of re-- contacts 17 of switch R, armature brush 19 to brush 21, contacts 18 of switch R,

' through the starting resistance B and to the main. The motor now starts to rotate and as its speed increases its counterelectro-motive force rises until the accelerating magnet is enabled to close one of its contacts. This results in a short circuiting of a portion of the starting resistance followed by a further increase in motor speed and attendant counter-electro-motive force, and the accelerating magnet is thus enabled successively to short circuit the entire starting resistance in a plurality of steps and the motor quickly runs up to full normal speed. It will be noted that the magnet winding of relay 30 is at this time short-circuited by the reversing switch contacts 17 and will not be operated, consequently the magnet winding of relay 20 receives current at the full potential of the motor armature, and, after this potential has reached a predetermined amount as the motor accelerates in. starting, the relay 20 will raise its core and thereby open circuit the contacts 22. These latter contacts are connected in the circuit of the winding of reversing switch R, hence it follows that it becomes impossible to raise the reversing switch R while the motor is rotating at an appreciable speed with the reversing switch R in closed position. If the operator attempts suddenly to reverse the motor by throwing the controlling switch S from one side to the other, it will 35 be seen that this operation merely opens the circuit of the magnet of switch It at the contact 11 but does not close a circuit to the other reversing switch R since the relay '20 will remain in raised position until the poential and speed of the motor undergoes a substantial reduction or until the motor ractically comes to rest. As soon as the re-- ay 20 is enabled to drop its core so as again to short circuit the contacts 22, a circuit may then be closed to the magnet of the reversing switch It and the motor reversed.

If the controlling switch S be moved ofi of the contact 11 to stop the motor while the latter is running at full s eed, and the operator changes his mind an at once moves his switch lever back onto contact 11 for the purpose of continuing the trip, the reversing switch R will first simultaneously open the )motor and. the accelerating magnet circuits 5 and immediately close sald circuits before the motor has had time substantially to reduce its speed. The starting resistance is of course reinsertedin the motor circuit butis rapidly cut out again, ro'viding the speed of the motor has not con materially reduced. Hence the motor is protected against a sudden rush of current when the motor circuit is'temporarily interrupted. -Whileit' is most desirable and necessary to wait for the motor to slow down before the operator can effect a reversal of the motor so as to prevent a sudden rush of current, and to prevent all shocks and jars to the motor and 113s connected load, such as the elevator car, it is also most desirable to enable the operator to open the motor circuit and again close it in the same direction without having to wait for the counter-electro-motive force and s eed of the motor to die out. This results in a substantial saving of time, which, as before pointed out, is-of decided advantage in the great majority of cases and particularly so in the case of electric elevators.

The operation of the system in a reverse direction is similar to that just described; the relay 30 .being automatically operated to prevent a too sudden reversal of the motor by the closing of the reversing switch R while the reversing switch R may be opened and closed whenever desired.

I prefer to construct the relays 20 and 30 as shown in Fig. 2, in which the screw plug 23 may be moved so as to vary the air gap between it and the magnet core 24, and in this manner the relay may be set or adjusted to operate on a current of a predetermined potential. In other words the relay may be adjusted so as to open circuitits contacts as soon as the motor commences to generate an appreciable counter-electro-motive force, or if desired the relay will not operate until the motor has run up to, say, one quarter speed, or more. The nuts 25, are threaded on the core 24 and may be adjusted so that the lift of the core may be varied so that the latter will drop at a predetermined motor potential and short circuit the relay contacts. other suitable resilient material is preferably located on the core as shown, so as to act in the nature of a cushioning device or buffer, and thereby enable the relays to operate noiselessly.

A- washer 26 of leather, rubber or While I have described my invention with when, the power circuit to the motor is opened at the reversing switches since the arrangement and electrical connections, for the same are wellknown in the art and form no part page of the invention.

. I desire not to" be limited to the precise construction and arrangement of parts herein disclosed, since it is obvious that one skilled in the art could readily make changes and alterations therein without'depermitting the energization of the other electromagnet while the motor is rotating.

2. The combination with an electric motor, of electromagnetic reversing switches therefor, a separate relay for controlling the operating circuit of each reversing switch, one relay operable at a predetermined speed of the motor, while the other relay will not operate until the motor is substantially at rest.

3. The combination with an electric motor, of electromagnetic reversing switches therefor, a separate relay for controlling the operating circuit of each reversing switch,

means controlled by the motor for effecting the operation of one relay, and means for preventing the operation of the other relay until the motor is substantially at rest.

4. The combination with an electric motor, of electromagnetic reversing switches therefor, a separate relay for controlling the operating circuit of each reversing switch, means controlled by the motor for effecting the operation of one relay, and means controlled by one of the reversing switches for preventing the operation of the other relay until the motor is substantially at rest.

5. The combination with an electric motor, of a pair of electromagnetic reversing switches. therefor, a separate relay controlling the operating circuit of each reversing switch,means for controllin said relays in accordance with the speed 0 the motor, and

means dependent upon the operation of a reversing switch for preventing the operation of one of said relays whereby a circuit may beclosed to the magnet of one revers ing switch at any speed of the motor but preventing the operation of the other reversing switch until the motor substantially comes to rest.

6. In a system of motor control, the combination of a motor, reversing switches, an operating circuit for each switch, and a relay for each operating circuit permanently connected to the motor controlled by the speed of the motor for maintaining but one of the said operating circuits open until such speed is substantially reduced. l

7. In a system of motor control, the combination of a motor, reversing switches, an operating circuit for each switch, a separate relay controllingeach operating circuit, the windings of said relays being connected in series across the motor armature, means for effecting the operation of one relay to open the operating circuit of one reversing switch to prevent a sudden reversal of the motor, and means for short circuiting the winding of the other relay so as to permit closing the operating circuit of the other reverslng switch. 1

8. In a system of motor control, the combination of a motor, reversing switches, an operating circuit for each switch, a separate relay controlling each operating .circuit, means for closing either operating 01?- cuit through the contacts of a relay, and means controlled by the motor for effecting the operation of but one of saidrelays.

9. In a system of motor control, the combination-of a motor, reversing switches, an operating circuit for each switch, a separate relay controlling each operating circult,

means for closing either operating circuit' through the contacts of a relay, means controlled by the motor for effecting the oper tion of but one of said relays, and means for adjusting said, relays so that they will operate at a predetermined potential both GEORGE N. CRABBE.

Q Witnesses WALTER C. STRANG, JAMES G. BETHELL.

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