US2305341A - Motor controller - Google Patents

Description

1942- c. P. FELDHAUSEN ET AL 3 3 MOTOR CONTROLLER Filed Nov. 8, 1939 15mm) I 8. @Mmmw Patented Dec. 15, 1942 UNITED STATES PATENT} OFFICE MOTOR CONTROLLER Cyril P. Feldhausen and Edwin W. Seeger, Wauwatosa, Wis., assignors to Cutler-Hammer, Inc., Milwaukee, Wis., a corporation of Delaware Application November 8, 1939, Serial No. 303,436

8 Claims. (01. 172--274) This invention relates to a motor controller and is particularly applicable to the control of motors whose speed must be varied between wide limits, and which must be capable of operating at a given very low speed for different torques required of the motor. If, for instance, a slip ring induction motor is used for driving a printing press, it is necessary to reduce the speed of such motor to as low as fifteen per centof the synchronous speed and yet accurately maintain this low speed and avoid stalling of the motor for any condition of torque required to drive the press, such torque varying Within wide limits for different jobs performed by the press. Hence a very high regulating resistance is required for a low torque and if this resistance is in the motor circuit when the torque is high, the motor stalls.

It is well known that the torque of a printing press and the like remains constant throughout a wide range of speeds for a given job and only varies for different jobs, and the present invention is intended for such service.

An object of the invention is to provide a controller, which, after the motor has been energized, automatically adjusts the speed regulating resistance in accordance with the torque requirement to provide for a given low speed.

Another object is to provide a controller which adjusts the regulating resistance in a step by step manner to prevent overrunning and hunting.

Another object is to provide a controller which is rapid in action to check tendencies of the motor to hunt.

Another object is to provide a controller which is easily adjusted to keep any desired low speed constant.

Other objects and advantages will hereinafter appear.

The accompanying drawing is a diagrammatic illustration of an embodiment of the invention.

A three phase slip ring induction motor I having a primary Winding l and a secondary winding l which latter is provided with terminals A, B and C, may be connected to a three phase supply source L L L by a switch 2. The control circuits are supplied with current from the bus bars L L of a source of supply of any suitable type. Variable slow speed resistors 3, 4 and 5 have one of their respective terminals connected together to form a neutral point 6, while the other terminals are each connected in series with a variable high speed resistor 1, 8 and 9, respectively, to one of the terminals A, B and C of the three phase secondary winding I of the;

motor and are also directly connected to three stationary contacts Ill Ifl Mi respectively, of an electromagnetic switch in. Said switch is provided with an energizing winding l W, a bridging contact Ill adapted to bridge the aforementioned stationary contacts when the switch is energized, and with normally closed contacts lt The aforementioned resistors are commutated by a contact brush H which travels back and forth over the resistors to short circuit a smaller or greater part thereof, first gradually short circuiting the resistors 3, 4 and 5 and upon further travel the resistors l, 8 and 9. The brush H is insulatedly attached to a traveling nut [2 which engages a screw 13 and is reciprocated thereby. The screw is connected through gears i4 and Hi to a reversible motor 15 which is provided with a lead I6 connected to L and reversing leads I 6* and l6 so arranged that when one or the other is connected to line L5 the'motor is energized to revolve inone or the other direction. Attached to a shaft extension of the screw I3 is a commutator I! which comprises two circular rings I! and ll interrupted at one point of their circumference and which are electrically connected together but insulated from the screw.

Contact brushes li and l'l normally engage the rings.

The system also comprises a normally open on push button it and a normally open off push button 19, an electromagnetic relay 2%, having an energizing winding 26 normally open contacts 26 and 29 and normally closed contacts 20; a relay 2|, having an energizing coil 2P normally open contacts 28 and normally closed contacts 2l; a relay 22 having an energizing coil 22 and normally open contacts 22, 22 and 22 a relay 23, having an energizing winding 23 normally open contacts 23 and normally closed contacts 23. A relay 24 has an energizing winding 24 and a rotating armature 24 which is rotated by the magnetic pull due to the energization of said winding in a counterclockwise direction against the pull or a biasing spring 24. The armature is provided with a shaft M which carries a contact lever 24 the latter being adapted to make circuit in its extreme positions with the stationary contacts 2 and 24 respectively.

Mounted on an insulating support parallel with the screw 13 are contact segments 25, 26 and 21, respectively. These segments are of varying lengths as will be explained hereinafter, While: contact buttons 25 23 and 21 respectively, are provided in alignment with the segments for contact with a contact brush 28 which motor operates at a relatively high speed. A

circuit is completed from line L over contact 25, brush 28, contact 21, coil 23 to line L Relay 23 is thus energized and keeps its contact 23 open and contact 23 closed. Contacts 23 when opened insert resistance 3! in series with coil 24 in a circuit from terminal C, over resistor 3|, resistor 32, coil 24 to terminal B. However, due to its speed, the secondary voltage of the motor is too low to operate relay 24 against the biasing spring 24, so that lever 24 is in contact with contact 24. Closure of contacts 23' completes a circuit from L over contacts 23 coil Hi, to L Thus contact m ridges contacts W, Hi which short circuits the terminals of resistors 3, 4 and 5, but this short circuit is inefiective, as these resistors are also short circuited together with part of the resistors 'l, 8 and 9 by the brush II.

If it is now desired to increase the speed of the motor, the operator pushes button It, thereby completing a circuit from L over contact l8, through coil 29, contacts 2| to L Relay 2!] is thereby energized to connect motor l6 across L L through contacts 20", while opening of contacts 26 prevents simultaneous energization of relay 2i. As soon as the motor it starts the nut l2 travels upward and the brush ll cuts out more of the resistors T, 8 and 9, thus speeding up the motor I. At the same time the brushes l'l and IE make contact with the rings I? and IT, respectively, thereby completing a path in parallel to button I8 from L through contacts 2% over rings H and IT Thus the operator may release the button and the motor I6 continues to rotate until the screw l3 has completed a revolution. If the operator continues to maintain the button l8 closed, the motor continues to operate and to reduce the resistance in the motor secondary circuit.

If it is desired to decrease the speed of the motor I, or if it is desired to move crosshead l l, 28 to its lowermost position, this may be effected by closing and/or holding closed the push button switch 19, thereby completing a circuit from L through said switch 19, coil 21 to L Relay 2! is thereby energized to connect motor Iii across L L through contacts 21 whereas opening of contacts 28 of relay 2! prevents simultaneous energization of relay 20.

Thus if the motor is started and is to be operated at the lowest steady speed for which relay 24 is adjusted, the crosshead is moved from its lowermost position to its first running position. Thus the secondary voltage is high enough to energize relay 24 to move lever 24 into contact with button 24 to energize relay 22 through a circuit from L over segment 25, brush 28, contact buttons 21 resistor 29, contact 2%, lever 2:1, coil 22 to L whereupon the relay maintains itself through contacts 22 and resistor 30 and also energizes relay 23 and relay 2E9. lRelay causes rotation of motor l 6 and thereupon maintains itself through contacts 22 and commutator I! while switch I0 is also energized by relay 23 and thus short-circuits that part of resistors 3, 4, 5 which is not short-circuited by brush H. Due to the aforementioned action of switch IS the motor I accelerates and the rotor voltage decreases so that the relay 24 short-circuits coil 22 by lever 24 making contact with 24. However, simultaneous operation of relay 20 in the manner aforedescribed causes rotation of screw [3 for one revolution (by reason of the circuit maintained through commutator 11), whereby a part or step of the resistances 3, 4 and 5 is shortcircuited by upward movement of brush II. If, however, the speed of motor I provided by such setting or adjustment of brush II should still be too low, the motor will temporarily decelerate and increase the rotor voltage until the same is high enough to again energize relay 24 in a manner to cause re-engagement of lever t l with button 24 thus repeating the aforedescribed operation-so that at each cycle of operation the amount of secondary resistor which is shortcircuited by the switch Iii is less until the relay 24 does not respond any more to energize relay 22 and the resistance in the motor secondary circuit is substantially the amount to operate it at the constant slow speed for which the relay 24 is adjusted.

To modify the amount of rotor resistance which corresponds to the adjustment of the relay 24 a greater or lesser number of the contact buttons 2'6 and 21* may be connected to the respective circuits so as to determine the lowest position in which the brush H is efiective to control the rotor resistance as aforedescribed. When the relay 23 operates in response to the energization of relay 22 by action of the voltage relay 24, relay 23 inserts resistance 3| in circuit with coil 24 and short-circuits said resistance again when the voltage of the motor is low enough to cause deenergization of relay 23 by the action of relays 24 and 22. This, as will be obvious, narrows the range of relay 24 to make it more sensitive.

Thu the controller, when the motor is to operate at its lowest practical operating speed, will automatically adjust the resistors to maintain such speed, the resistor being automatically varied with variations of the torque which the motor exerts.

Obviously the pilot motor may be replaced by other operating means. Also the step by step motion of the commutator may be dispensed with Without departure from the essence of the invention, and the voltage responsive relay may be replaced by suitable speed responsive means.

What we claim as new and desire to secure by Letters Patent is:

1. A controller for controlling the speed of an electric motor operable in a high speed range and in a low speed range respectively, and driving a load whose torque in the low speed range is substantially constant, comprising, in combination with a motor, a regulating resistor adapted to be connected in circuit with said motor and having a section effective only during low speed operation of said motor, means operative to gradually vary the effective value of said resister, and automatic means responsive to speed variations of said motor, including short-circuiting means effective during low speed operation of said motor for commutating the part of said section which is left in circuit by said first mentioned means and simultaneously to effect operation of said first mentioned means to vary the effective resistance of said part, and to terminate response of said short-circuiting means when all of said section of said resistor is cut out of circuit by said first mentioned means.

2. A controller for controlling the speed of an electric motor operable in a high speed range and in a low speed range, respectively, and driving a load whose torque in the low speed range is substantially constant, comprising, in combination with a motor, a regulating resistor adapted to be connected in circuit with said motor and having a section effective only during low sped operation of said motor, means for varying step-by-step the effective value of said resistor,

a manual switch for controlling said step-by-step means, automatic means responsive to speed variations of said motor, and short-circuiting means under the control of said last mentioned means effective during low sped operation of said motor for commutating a part of said section which is left in circuit by said first men tioned means and simultaneously to effect operation of said first mentioned means to vary the effective resistance of said part, and to terminate response of said short-circuiting means when all of said section of said resistor is cut out of circuit by said first mentioned means.

3. A controller for controlling the speed of an induction motor having a secondary winding and operable in a high speed range and in a low speed range respectively, and driving a load whose torque in the low speed range is substantially constant, comprising, in combination with an induction motor, a variable resistor adapted to be inserted in the secondary circuit of said motor, and having a section effective only during low speed operation of said motor, means operative to gradually vary the effective value of said resistor including step-by-step driving means for actuating said first mentioned means, a relay adapted to respond to the voltage of the secondary winding of said motor, electromagnetic means responsive to the operation of said relay, effective during low speed operation of said motor for commutating a part of said section which is left in circuit by said first mentioned means and simultaneously to effect operation of said driving means, and to terminate response thereof when the operation of said commutating means becomes ineffective to further change the effective value of said section.

4. A variable speed motor control system comprising, in combination, a motor having an armature circuit, a variable resistance in said circuit and having an operating elememt including a contact brush to vary said resistance, a re versible motor for operating said element, a voltage relay connected to said armature circuit, an electromagnetic switch controlled by said relay and adapted to commutate a given section of said resistance independently of said brush, and electromagnetic means under the control of said relay and said switch and adapted to en ergize said reversible motor simultaneously with the commutation of said resistance by said switch while such commutation of said section is effective to change the effective value of the resistance in the armature circuit.

5. A variable speed motor control system comprising, in combination, a motor having an armature circuit, a variable resistance in said circuit and having an operating element including a contact brush movable to vary said resistance, reversible motor means for moving said element step by step, a voltage relay connected to said armature circuit and responsive to the voltage thereof, an electromagnetic switch controlled by said relay and adapted to control a given section of said resistance independently of said con tact brush, and electromagnetic means under the control of said relay and said switch and adapted to energize said reversible motor for movement of said brush while the control of said section by said switch is effective to change the effective value of the resistance in said armature circuit.

6. A controller for controlling the speed of an electric motor, operable in a high speed range and in a low speed range respectively, and driving a load whose torque in the low speed range is substantially constant, comprising, in combination with a motor, a motor regulating resistor adapted to be connected in circuit with said motor and having a section effective only during low speed operation of said motor, means operative to vary the effective value of said resistor, automatic means responsive to speed variations of said motor, including short-circuiting means effective during low speed operation of said motor for commutating the part of said section which is left in circuit by said first mentioned means and independent thereof, to thereby maintain the motor speed substantially constant, and said automatic means being adapted to simultaneously effect operation of said first mentioned means to vary the effective resistance of said part, and to terminate response of said short-circuiting means to said speed responsive means when all of said section of said resistor is cut out of circuit by said first mentioned means.

7. A controller for controlling the speed of an electric motor operable in a high speed range and in a low speed range, respectively, and driving a load whose torque in the low speed range is substantially constant, comprising, in combination with a motor, a motor regulating resistor adapted to be connected in circuit with said motor and having a section efiective only during low speed operation of said motor, means operable to vary the effective value of said resistor step-by-step, a manual switch for controlling said step-by-step means, automatic means responding to speed variations of said motor and including short-circuiting means effective during low speed operation of said motor for commutating independent of said first mentioned means the part of said section which is left in circuit by said first mentioned means to thereby maintain the motor speed substantially constant, and said automatic means being adapted to simultaneously effect operation of said first mentioned means to vary the effective resistance of said part, and to terminate response of said short-circuiting means to said speed responsive means when all of said section of said resistor is cut out of circuit by said first mentioned means.

8. A controller for controlling the speed of an induction motor having a secondary winding and operating in a high speed range and a low speed range respectively and driving a load whose torque in the low speed range is substantially constant, comprising, in combination with an induction motor, a variable resistor adapted to be inserted in the secondary circuit of said motor and having a section effective only during low speed operation of said motor, means operative to gradually vary the effective value of said resistor including step-by-step driving means for actuating said first mentioned means, a relay adapted to respond to the voltage of the secondary winding of said motor, electro-magnetic means responsive to the operation of said relay and effective during low speed operation of said motor for commutating a part of said section which is left in circuit by said first mentioned means and simultaneously to effect operation of said driving means and to terminate response of said driving means when the operation of said resistance varying means becomes inefi'ective to further change the efiective value of said section.

CYRIL P. FELDHAUSEN. EDWIN W. SEEGER.

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