US1562968A - Motor-control system - Google Patents

Description

Nov. 24, 1925. 1,562,968

' B. W. JONES MOTOR CONTROL SYSTEM Filed May 6. 1924 Fig.2.

' InJefitow: Ber iamin \MJoneS,

M TA

His Attorney.

Patented Nov. 24, 1925.

UNITED STATES 1,562,968 PATENT OFFICE.

BENJAMIN W. J ONES, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAIl ELEG- TRIC COMPANY, A CORPORATION OF NEW YORK.

MOTOR-CONTROL SYSTEM.

Application filed May 6, 1924. Serial No 711,494.

T all whom it may concern:

.Be it known that I, BENJAMIN WV. JoNEs,

a citizen of the United. States, residing at Schenectady, in the county of Schenectady, 8 State of New York, have invented certain new and useful Improvements in Motor- Control Systems, of which the following is a specification.

My invention relates to systems of control 10 means whereby the motors are started and smoothly accelerated under Widely varying service conditions.

One of the objects of the invention is to provide an improved arrangement whereby the motor is controlled in response to the rate of change of an operating condition, such, for example, as the rate of change of the motor speed or the rate of change of an electrical characteristic of the motor or the motor circuits which is responsive to the rate of change of the speed of the motor.

Although the invention is not necessarily limited thereto, it has a particular application in systems of direct current motor control wherein the control of the motor is effected by means of resistance in series with the motor armature and other resistance arranged to be connected in shunt to the motor 30 armature. A common form of control having resistance in series with the motor armature and another resistance in shunt thereto employs switch mechanism for controlling the resistance so arranged that sections of the 35 resistance are alternately included in shunt to the motor armature as sections of the resistance in series with the motor armature are short-circuited during the acceleration of the motor. A common arrangement of this sort is one in which double throw electromagnetic switches or contactors are provided, each switch arranged to normally short-circuit a section of shunt resistance and when energized to remove the shortcircuit about the section of shunt resistance and short-circuit a section of the series resistance. Thus, a. section of the resistance is cut into the shunt circuit about the motor armature substantially simultaneously with cutting out a section of the resistance in series with the motor armature. Arrangements of this sort are objectionable because of the inflexibility thereof. Thus, in case the control system is employed for governing an electric motor driving an for electric motors and it provides improved elevator, hoist or the like, if the operator does not use care and intelligence in the manipulation of the master switch controlling the electromagnetic resistance switches, he is apt to effect a too rapid operation oi the resistance switches. If the operator manipulates the master switch so as to start the elevator moving down with a heavy load on the elevator and moves the master switch from the off position towards the maximum speed down position very slowly, the electromagnetic switches would alternately vary the shunt and the series resistances with sufiicient interval between the one step of the control to the next, so that the elevator is accelerated smoothly and gradually. However, if the operator turns the controller rapidly from the OK to the maximum speed down position, a very high accelerating torque is applied to the motor, in addition to the high over-hauling load torque and this causes a very rap-id acceleration of the elevator which'is objectionable. In accordance with my invention, I provide a flexibility between the successive steps of including a. resistance in shunt to the motor armature and short-circuiting a resistance in series with the motor armature, so that at least one of the resistances will be governed not only in response to the prior operation of varying the other resistance but also in response to the rate of change of an operating condition of the motor or the motor circuit, such for example as the rate of change of the counter electromotive force of the motor.

In accordance with the invention in the form which I now regard as the preferred form, if the operator manipulates the master controller very quickly, the short circuiting of the series resistance will not immediately follow the inclusion of resistance in shunt to the motor armature, as in prior arrangements, but will be delayed depending upon the rate of change of the counter electromotive force of the motor, so as to thereby permit the motor to accelerate smoothly and automatically prevent increasing the accelerating torque too rapidly. If the op erator manipulates the master controller slowly, the operation of the equipment will be substantially the same as the said prior arrangement, namely, the series resistance will be out out substantially simultaneously with the cutting in of the resistance in shunt to the motor armature. If the load is to be hoisted, the rate of change controlling devices connected and arranged in accordance with the invention will permit the series resistance to be short-circuited step by step p in a more rapid sequence than in the ease of starting the elevator down with a heavy over-hauling load, and the motor-is thereby forced to accelerate its'load at the correct rate. In other words, the control in accordance with the invention automatically takes care of such varying conditions as the variations of the speed of operation of the master controller, the variations in the value of the load on the elevator, as to whether or not the load is being hoisted or lowered, and as to whether or not the load is over-hauling or otherwise.

For a better understanding of my invention, reference is had to the following description taken inconnection with the V accompanying drawing in which Fig. 1 is a sim lified diagram illustrating a motor contro system embodying my invention for the purpose of explaining the principles thereof, and Fig. 2 diagrammatically illustrates a reversing motor control system suitable for elevator service, likewise embodying the invention.

The novel features which I believe to be characteristic of my invention are set forth with articularity in the appended claims. Re erring first to Fig. 1 of the drawing, the motor 10 which is controlled according to my invention is shown as of the direct current type having an armature 11 and a shunt field winding 12. The resistances 13 and 14 are connected respectively in series and in shunt with the armature 11 and are of suitable ohmic value to limit the motor to a desired low speed when the normally open electro-magnetic line switch 15 is closed to connect the motor 10 to a suitable source of supply. The normally closed electromagnetic switch 16 is connected in circuit with the shunt resistance 14 and is operable to the open position to interrupt the circuit through the resistor 14. The manually operable master controller 17 is provided for controlling the energizing circuits of the electromagnetic switches 15 and 16;

In order to control the series resistance- 13 in-accordance with the rate of. change of the motor speed efl'ected by operation of the master controller 17, I provide the electroresponsive switch mechanism 18. In the preferred form shown, this electroresponsive switch mechanism is of the general type described and broadl claimed in my copending a plication or patent, Serial No. 595,875, fi ed October 20, 1922. ,It will be observed that this type of switch mechanism is provided with an energizing winding 19 and a short-circuited winding 20 which are arranged to cooperate in controlling the actuation of the pivoted contact member 21.. While this particular type of electroresponsive switch is well adapted for use in my resent invention I would have it understood that the present invention is not limited thereto since other types of electroresponsive switches may be employed if desired.

With-the arts in their respective osi tions shown in Fig. 1 the operation 0 my improved control system is as follows: Upon operating the master controller 17 to the first position, the winding of line switch 15 is energized and the switch'operates from the open position shown to the closedposition and connects the motor 10 to a suitable source of supply. As previously pointed out the series resistance 13 and the shunt resistance 14 limit thespeed of the motor 10 to a low value depending upon the relative ohmic values of the resistances 13 and 14, as well as the value of the load driven by the motor 10. Upon the further operation of master controller 17 to the second position, the electroma etic switch 16 is energized to open the s unt circuit around the motor armature 11 including the resistance 14. The resulting increase of current through the motor armature increases the motor tor ac and tends to accelerate the motor to a igher speed. Upon the opening its motive force correspondingly increases in value. Due to the inductive relation between the energizing winding 19 and theshort circuited winding 20, the latter is thereupon energized res'ponsively to the rate of change of the motor counter electromotive short circuited winding 20 is below the predetermined value. v

Should the motor be heavily loaded so as to accelerate slowly upon opening of the switch 16, the short circuited winding 20 will not be energized sufficiently to prevent the pivoted switch member 21' from being operated to the closed osition by the energizing winding 19. Un er these conditions the short circuits the series resistance 13, thereby further'increasing the motor torque to 'hasten the response of the motor 10 to the operation of master controller 17.

If, however, the motor is lightly loaded so as to be rapidly accelerated upon the opening of the manually controlled switch 16, the electroresponsive switch mechanism 18, then functions to delay the closing of the short circuit around the series resistance 13, while the rate of change of the motor speed and consequently the rate of change of its counter electromotive force is above a predetermined value. In this case, upon the opening of switch 16, and the resulting energization of the winding 19 responsively to the motor counter electromotive force, the short-circuited winding 20 is strongly energized and prevents the operation of the pivoted contact member 21 to the closed position by the energizing 'winding 19. After the acceleration of motor 10 has reached a substantially constant value determined by the value of the series resistance 13, and the rate of change of the motor counter electromotive force is below a predetermined value, the inductive energization of short circuited winding 20 is reduced to a value which permits the pivoted contact 21 to close and short circuit the series resistance 13. Thereupon the motor 10 is accelerated to full running speed.

Referring now to the reversing motor control system shown in Figure 2 of the drawing, it will be understood that for elevator service the armature 11 of the motor 10 is mechanically connected by means not shown in the drawing to drive an elevator car or other hoisting apparatus. The electromagnetic reversing switches 23 and 24, together with the electromagnetic line switch 25 are provided for connecting the motor 10 to the supply lines 26 and 27 for operation in either direction. In order to operate the motor 10 at a plurality of definite speeds with an overhauling load as well as an underhauling load the several resistances, 28, 29, 30, and 31 are connected in a shunt circuit across the motor armature 11, and

the resistances 32, 33, 34, 35, and 36 are connected in series with the motor armature 11. The shunt resistances 28, 29, 30 and 31 are controlled respectively by the normally closed electromagnetic switches 37, 38, 39 and 40 and these electromagnetic switches are arranged to be operated in a predetermined sequence under the control of the manually operated master switch 41 which also controls the energizing circuits of the electromagnetic reversing switches 23 and 24 and the electromagnetic line switch 25.

To automatically control the rate of change of the motor speed which may be effected by operation of the manually controlled master switch 41, the electroresponsive switch mechanism comprising in the preferred form shown the relays 42 and 43, each having an energizing winding 44 and 45 and a short circuited winding 46 and 47 respectively together with the normally opened electromagnetic switches 48, 49, 50,

51, and 52 which are provided for controlling the series resistances 32, 33, 34', 35 and 36 in a manner which best will be understood from the following description of the operation of the control system shown in Fig. 2. Each of the relays 42 and 43 is similar in design and construction to the electromagnetic switch 18 shown and described in connection with Fig. 1 and the short circuited windings 46 and 47 are in inductive relation with the energizing windings 44 and 45 respectively. It will be observed that the energizing winding 44 of the relay 42 is connected to the auxiliary contact 53 which is engaged upon the operation of the electromagnetic switch 37 to the open position and the energizing winding 45 of the relay 43 is also connected to a corresponding auxiliary contact 54 on the electromagnetic switch 39.

With the se eral parts thus constructed and arranged the operation of the control system shown in Fig. 2 is as follows: Assuming the supply lines 26 and 27 are connected to a suitable source, the motor 10 may be operated in the hoisting direction by moving the master controller 41 progressively to the positions indicated as 1, 2, 3, 4, 5, and 6 in the drawing. In position 1, an energizing circuit for the reversing switch 23 is completed from the supply line 26 through the contact segments 61 and 62 of master controller 41, the conductor 63, the operating winding of the electromagnetic switch 23 and the conductor 64 to the other supply line 27 and switch 23 is operated from the open position, to which it is biasedas shown, to the closed position and establishes connections for operating the motor 10 in the desired direction upon closure of line switch 25. In the second position of the master controller, a circuit is closed from the supply line 26 through the contact segments 61 and 66 of the master controller 41, the conductor 67 the operating winding of the electromagnetic line switch 25 and the conductor 68 to the other supply line 27. Upon the resulting closure of line switch 25, the motor armature 11 is con nected in series with the resistances 32, 33, 34, 35 and 36 to the supply line 26 and 27 with the resistance 28 connected in shunt with the motor armature 11 through the normally closed electromagnetic switch 37 the other shunt resistances 29, 30 and 31 being short circuited at starting. As the master controller 41 is moved into the third position an energizing circuit for the'operating winding of the electromagnetic switch 37 is completed from supply line 26 through the contact segments 61 and 69, the conductor 70, the operating winding of switch 37 and the conductor 68 to the other supply line 27. Thereu on the electromagnetic switch 37 'respon s to open the shunt circuit through .the resistance 28 and to connect the energizing winding 44 of the remotor counter electromotive force to prevent closure of the relay contact when the motor accelerates rapidly due to the opening of switch 37. In either case the relay 42 closesits contact when the rate of change of the motor speed-is below a predetermined value and thus establishes an energizing circuit for the operating winding of electromagnetic switch 48 from: the supply line 27, through the contacts of relay 42, the winding of switch 48, and the con.-

-ductor 71 to the other supply line 26.

Closure of switch 48 establishes a short circuit around the resistance.32, thus further accelerating the motor 10.

Upon closure of electromagnetic switch 37 an energizing circuit for' the electromagnetic switch 38 is established through the auxiliary interlocking contact 72 with which electromagnetic switch 37 is provided. Hence upon operation of the master controller 41 to the fourth position, the operating winding of switch 38 is energized through the contact segment 73, the conducfor 74, the auxiliary contact 72, the operating winding of electromagnetic switch 38' and the conductor 68 to the other supply line 27. Switch 38 thereupon operates to open the shunt circuit through the resistance 29 and thereby again increases the speed of motor 10. In a similar manner the electromagnetic switch 39 is energized through the auxiliary contact of electroma netic switch 38 and the contact segment 6 of master controller 41 when the latter is oper ated to the fifth position andopens the shunt circuit through the'resistance 30 and accelerates the motor 10 "to a higher speed. Opening of the switch 39 connects the energizing winding 45 of the electromagnetic relay 43 across the motor armature 11 and the short circuited winding 47' either permits the immediate response of the relay when the rate of change of motor counter electromotive force is below a predetermined value or delays the response of'the relay 43 in case the motorcounter electromotwe force is lncreasmg at a rate above the predetermined value, in exactly the same manner as was described in connection with the relay 37 Upon the response of relay 43 the switch 49 is energized through a circuit including the auxiliary contact83 of switch 48 and operates to. short circuit the resistance 33. The motor then may be accelerated to full running speed by operation of the master controller 41 to the sixth osition.- This effects the ener i'zation of t e electromag netic switch 40 t rough the contact segment 78 of the master controller and the auxiliary contact 79 on switch 39, and switch. 40 o erates from the closed position to open t e entire shunt circuit across the motor armature including the resistances 28, 29, 30 and 31. The auxiliary contact 80 with .which the electromagnetic switch 40 is provided completes the energizing circuit for 'the operat ng winding of electromagnetic .switch 50 which may be traced from the supply line 27 through the auxiliary contact 81 on electromagnetic switch 49, auxiliary contact 80 on switch 40, the winding .of electromagnetic switch 50 and through the conductor 71 to the other supply line 26. The successive operation of the electromagnetic switches 50, 51 and 52, to short circuit the ' series'resistances 34, 35 and 36 respectively thereupon occurs in an obvious manner since the successive energization of each switch is controlled by an interlocking contact which is closed upon operation of the preceding switch.

U on the return of the master controller 32 through the successive positions 6, 5, 4, 3 and 2, the resistance controlling switches :are progressively deenergized and returned to their respective positions shown thus again inserting the series and shunt resistances in circuit with the motor armature to decelerate the motor through a sequence of definite speeds, to its lowest operating speed.

Further movement of the master controller 41 through the position 1 to the off position shown interrupts the energization of line switch 25 and reversing switch 23 and brings the motor to a stop.

In order to operate the motor 10in the reverse or lowering direction, master controller 41 is operated to engage the right hand set of contact segments. In this case the electromagnetic reversing switch 24 is first energized through the contact segment 82 and the line switch 25 and the several resistance controlling electromagnetic switches are successively operated in exactly the same manner as previously described to accelerate the motor through a series of intermediate s eeds.

It should e notedthat if during the acceleration of the motor 10 in either direction as reviously described, the load on the motor s iould be such that the rate of acceleration after the -o eration of either the manually controlle electromagnetic switch 37 or 39, is below the value at which the short circuited winding 46 and 47 of the electromagnetic relays 42 and 43 res ectively are operatively energized, each 0 the relays immediately responds to efiect the short circuiting of the corresponding series resistances 32 and 33 to accelerate the rate of change of motor 10 produced by the closing of the electromagnetic switches 28 and 30 res ectively.

If, owever, an impetuous or careless operator should throw the master controller 41 from the off position to the full speed running position so that themotor is connected to the source of supply and the manually controlled electromagnet switches 37, 38, 39 and 40 are operated in rapid succession to accelerate the motor at a correspondingly rapid rate, each of the electromagnet relays 42 and 43 then operates to prevent the short circuiting of series resistances 32, 3'3, 34, 35 and 36 in the following manner. Upon the operation of the electromagnetic switch 37 to connect the energizing winding 44 of relay 42, across the motor armature, the short circuited winding 46 is thereupon inductively energized responsively to the rate of change of the motor counter electromotive force, as previously described. Hence, while the motor is accelerating due to the successive operation of the electromagnetic switches 38, 39 and 40, the short circuited winding 46 prevents the response of relay 42 and the consequent energization of the electromagnetic switch 48 to short circuit the series resistance 32. The relay 43 likewise is prevented from closing upon the operation of electromagnetic switch 39 by the short circuit winding 47.

Thus it will be seen that the series resistances 32, 33, 34, 35 and 36 are maintained in circuit with the motor armature and serve to prevent an unduly rapid response of the motor 10 to an improper operation of the master controller 32 such as assumed above.

When the rate of acceleration of motor 10 falls below at predetermined value, the short circuited winding 46 of relay 42 will not be energized sufiiciently to prevent closure of the relay contacts by the energizing winding 44 and the relay 42 thereupon responds to energize the electromagnetic switch 48 which operates to short circuit the resistance 32. After the motor 10 has again accelerated and reached a substantially constant speed, the short circuited winding 47 of relay 43 will be deenergized and permit the closing of relay 43, electromagnetic switch 49, 50, 51 and 52 in the regular order previously described.

It will be evident to. those skilled in the art that suitable limit switch mechanism as well as overload safety switch mechanism may be provided for protecting the motor 10 if desired.

In accordance with the provisions of patent statutes, I have described the rinciple of operation of my invention, toget or with the apparatus which I now consider to represent the best embodiment hereof, but I would have it understood that the invention may be carried out by other means.

What I claim as new and desire to secure by Letters Patent of the United States, is,-

1. In a motor control system, the combination of an electric motor, a resistance arranged to be connected in shunt to the motor armature, a resistance in series with the motor armature, a plurality of electroresponsive switches normally operable in a predetermined sequence for varying the said resistances to change the motor speed, and means operated responsively to the rate of change of the motor speed for preventing the operation of a portion of the said switches to vary one of said resistances when the change in the -motor speed exceeds a predetermined value upon the operation of another portion of said switches to vary the other of said resistances.

2. In a motor control system, the combination of an electric motor, a resistance arranged to be connected in shunt with the motor armature, a resistance in series with the motor armature, a plurality of electroresponsive switches for varying the said resistances, manually operated means for controlling the connection of the motor to a source of supply and for operating a portion of said switches to vary the said shunt resistance and thereby accelerate the motor, and means operated responsively to the rate of change of the motor speed for operating another portion of said switches to vary the said series resistance to accelerate the motor when the rate of change of the motor speed due to operation of the said first portion of the switches is below a predetermined value.

3. In a motor control system, the combination with the motor, of a plurality of resistances, one connected in shunt and another in series with the motor armature,

"switch mechanism for varying one of the said resistances to change the motor speed, an electromagnetic switch for controlling the other of the said resistances to change the motor speed, electric connections established upon the operation of said first switch mechanism for energizing a winding of said electrom etic switch responsively to anelectrical iiharacteristic of the motor which varies with the speed thereof, and means arranged to prevent response of said electroi cludin an electromagnetic switch controlled by sai first switch mechanism and having a winding energized responsively' to the rate of change of the motor which varies with the speed of the motor, and a second winding inductively related with said first winding to prevent operation of the switch to short circuit said series resistance while the rate of change in said electrical characteristic is above a predetermined value.

5. In a motor control system, the combination with the motor, of a plurality of resistances, one connected in shunt and another in series with the motor armatures, switch mechanism operable between two positions for controlling one of said resistances, and an electromagnetically actuated switch for controlling another of said resistances and havin an operating winding energized responsive y to the counter electromotive force of the motor upon operation of said first switch mechanism to one position and a short circuited winding inductively energized from said first winding for delaying operation of the switch while the rate of c ange of the motor counter electromotive force is above a predetermined value.

6. In acontrol system, the combination of an electric motor, a plurality of resistances connected in circuit with the motor for controlling the speed thereof, one of said resistances being connected in shunt with the motor armature and another of said resistances being connected in series with the motor armaan electrical characteristic of v open position an ture, switch mechanism for connecting the motor to a source of sup ly for o ration thereof and for varying said unt re sistan' ce to acceleratethiei motor;i a havanen win ngan aso cirb u ted wiiib iifg an electromagnetic switch biased to the open position and having an operating wind-mg controlled. by said relay for establishing a short circuit around the said series resistance, and electrical connections controlled by said switch mechanism for connecting the energizing winding of said relay across the motor armature w e by the said short circuited windin is energized responsively to the rate of c ange in the counter electromotive force of the motor to prevent the short circuiting of said series resistance while the rate of acceleration of the motor is above a predetermined value. 7. In a control system, the combination of an electric motor, a plurality of resistances, one connected in shunt and another in series with the motor armature, an electromagnetic switch connected" in circuit with said shunt resistance and biased to the closed position, a second electroma netic switch biased to the operable to the closed position to establish a short circuit around the said series resistance, a master switch for connecting the motor to a source of supply and for controlling the operation of. said first electromagnetic switch, a relay for controlling the energizing circuit of said second electromagnetic switch, said relay having an energizing winding and a short circuited winding, and electrical connections whereby when the said first electromagnetic switch is operated to the open position, the said energizing winding of said relay is connected across the motor armature and the said short circuited winding is energized responsively to the rate of change in the counter electromotive force of the motor to prevent the energization of said second electromagnetic switch when the rate of acceleration of the motor is above a predetermined value. a a v In witness whereof, xI have hereunto set my hand this 5th day of May, 1924.

BENJAMIN w. JONES..

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