US2022535A - Motor control system - Google Patents

Description

NOV. 26, 1935. BYLES ET AL 2,022,535

MOTOR CONTROL SYSTEM Filed Sept. 24, 1931 Invenbovs Fwank A.B qles. FF (1 H.\A/inber*,

Their Abtomne Patented Nov. 26, 1935 PATENT OFFICE MOTOR CONTROL SYSTEM Frank A. Byles, Scotia, and Fred 11. Winter, Schenectady, N. Y., assignors to General Electric Company, a corporation of New York Application September 24, 1931, Serial No. 564,896

'IOlalms.

Our invention relates to motor control sysiems. more particularly to systems for governing the operation of rotary grinding machines used in the production of wood pulp, and has for an object the provision of a reliable automatic system responsive to changing conditions incident to the operation of the machine for insuring a uniform product.

While our invention is not necessarily limited thereto, it is particularly applicable to the type of grinding machine employed in the production of wood pulp to be used in the manufacture of paper. A typical machine of this type consists of a grindstone carried by a rotary driving. shaft to which the wood in the form of short logs is fed by a suitable feeding means. Although the surface condition of the grindstone and the amount of water supplied to the stone must be considered, the texture of the wood pulp obtained from the grinding machine is dependent to a large degree on the pressure with which the wood or logs are urged against the grindstone. By maintaining the pressure substantially constant the texture of the wood pulp is much more uniform than when the pressure varies above and below a predetermined amount. Uniformity of the wood pulp is particularly desirable since at the present time the practice is to use the wood pulp as obtained from the grinding machine for paper manufactures.

In carrying out our invention in one form, we provide for the feeding of the wood against the grindstone so that a substantially constant predetermined pressure of the wood against the grindstone is maintained. More specifically, we utilize the oil pressure at the bearings of the grindstone in conjunction with a vibratory regulator to control the drive of the feeding means for the wood. The vibratory regulator is of the type which prevents over-regulation of the feeding means and thereby insures a more uniform texture of the wood pulp.

For a more complete understanding of our invention, reference should now be had to the drawing, the single figure of which diagrammatically shows our invention applied to a control system for a wood pulp grinding machine.

Referring to the drawing, we have shown our invention in one form as applied to a Ward- Leonard control of a motor i8 arranged to drive the endless feed chains l I and I2 through the cooperation of the gears l3 and I4 secured to the motor shaft and the gears l5 and i8, respectively, driving the feed chains ii and I2. Billets of wood, or short logs, are introduced between the feed chains and are urged downwardly to engagement with a grindstone l1. The operations of the motor III are controlled by a generator i8 whose armature is connected in local circuit with the armature of the motor. A generator 5 field winding I8 is connected to the armature of the generator and through a resistance 20, a reversing switch 2|, and a resistance 22 to a separate source of direct current supply as indicated by the supply lines 23 and 24.

For the purpose of controlling the speed and direction of rotation of the motor ill, the bearing oil pressure of the grindstone i1 is transmitted through a pipe 25 to a Bourdon pressure element 28 operatively connected to a lever 21 which is 15 pivoted at 28 and which supports on opposite sides of the pivot contacts 29 and 30. A contact 3| carried by a lever 32 pivoted at 33 is arranged to cooperate with the contact 30 which is suitably insulated from the lever 21. 'An anti- 20 hunting electromagnet 34 energized by the voltage of the generator I8 is arranged to increase the distance between the contacts 30 and 3| while the springs 35 and 36 are arranged to oppose the pull of the electromagnet 34. The closing of the con- 25 tacts 30 and 3i causes the energization of a coil 31 connected in opposition to a coil 38. The coil 38 normally maintains the relay 39 open, the resistance 20 thereby remaining in circuit with the field l3. It will be observed that whenever the 30 contacts 38 and 3! close, the coils 31 and 38 neutralize each other so that a spring 40 connected to the armature of the relay 39 thereupon operates the relay to its closed position. The efiect of closing the relay 3!! is to shunt the resistance 35 28 from the field circuit causing an increase in the excitation and output of the generator i8. The resulting increased speed at which the motor l8 drives the feed chains II and I2 correspondingly increases the pressure of the wood against 40 the grindstone.

The contacts 29 and 4| are arranged to be closed whenever the pressure against the grindstone drops below a predetermined amount. The contacts of a differentially operated relay 42 are 45 connected in series with the contacts 29 and 4|. The contacts of the relay 42 are closed by a spring 43 whenever the generator current responsive coil 44 neutralizes the effect of the generator voltage responsive coil 45. The circuit thereby completed serves to energize a relay 46 which operates to complete a circuit to operate the reversing switch 2! and to initiate the operation of a timing mechanism 41.

with the above identification of the elements 55 comprising an embodiment of our invention, the operation will be fully understood by the detailed description which follows: In the operation of our invention in the form shown it will be assumed that the grindstone I1 is being driven at constant speed by a suitable prime mover shown as an alternating current motor I and that short logs of wood have been introduced between the drive chains II and I2. It will also be assumed that the generator 48 is being rotated at constant speed by a suitable prime mover (not shown). It will be observed that the generator field winding i9 is energized from the direct current supply lines 23 and 24 through a circuit which may be traced from the supply line 23, conductors BI and ii, the upper contact of the switch 2i, conductor l2, resistance 20, field winding IO, through the armature of the generator l8, conductors 53 and 54 to the lower contact of the switch 2!, conductor 55, to an adjustable tap 220 provided on the resistance 22, through a portion of the resistance 22 and by conductor 56 to the other supply line 24. The resistor 22 furnishes a small starting voltage to initiate the rise of magnetism in the generator. Thereafter the rising voltage of the generator ll causes excitation current to fiow through the field winding l9 through a circuit which may be traced from one side of the armature of the generator I! by conductor 53, conductor 54, the lower contact of the switch 2|, conductor 55, through the upper portion of the resistance 22 by conductor 5i to the upper contact of the switch 2 I, thence by conductor 52 and the resistance through the field winding l9 and to the other side of the armature of the generator It.

The consequent excitation of the field winding l9 causes the generator voltage I! to build up which in turn causes the motor III to rotate in the proper direction to drive the feed chains and to urge the wood against the grindstone H. The local circuit between the motor and generator armatures may be traced from one side of the generator armature by conductor 60, through a resistance 62 and a coil 44 connected in parallel with each other, thence by conductor 63 through the motor armature and by conductor 64 to the other side of the generator armature It. The field winding 65 provided on the motor III is directly connected across the supply lines 23 and 24.

It will be observed that the coil 38 of the field controlling relay is is directly connected through a resistance 10 to the conductors 50 and 56 leading from the supply lines 23 and 24, the coil being arranged to maintain the relay 38 open. The resistance 20 is therefore normally connected in circuit with the field winding l9 causing the motor iii to rotate at a lower speed than when the resistance 20 is short-circuited. If the pressure on the grindstone I! decreases below a predetermined amount the Bourdon pressure element 26 closes the contacts 30 and SI, thereby energizing the coil 31 through a circuit which may be traced from the supply line 28, conductor 50, resistance 10, conductor II, contacts 39 and 3i, conductor 12, coil 31, conductor 13,

conductor 56 and to the other supply line 24. In-

asmuch as the coils 31 and 38 are difierentially connected, the switch 39 is thereby closed by reason of the tension spring 40 connected to the armature of the switch 39. The closure of the switch 39 short-circuits the resistance 20 and thereby increases the excitation of the generator is. The resulting voltage rise produces an increased motor speed so that the feed chains II and I2 driven by the motor drive the logs with greater effort against the grindstone II. It is to be observed, however, that the increased voltage corresponding to an increased output of the 5 generator II is applied to the anti-hunting magnet which causes thecontacts II and SI to separate against the bias of the springs II and 8'. The result is a vibratory motion of the lever 32 carrying the anti-hunting contact II. The 10 opening of the contacts 30 and Ii causes the opening of the relay 3! and hence the reinsertion of the resistance 20. As is well understood in the art, the excitation voltage of the generator II and consequently the speed of the motor It is 5 dependent upon the average time that the relay is and the contacts Ill and II are closed, which average time is dependent upon the relative positions of the lever 33 and the lever 21. The net result is a vibratory action of the part of the go relay is and the contact 3| with a consequent control of the excitation of the generator II which is precise and accurate and corresponds to the increased excitation necessary to cause the desired increase of pressure on the grindstone ll.

Were it not for the quick acting anti-hunting means, the regulator would tend to produce hunting with consequent periodic increases and decreases from the normal pressure of the wood against the grindstone. Thus, assuming conso tact II to be fixed, the engagement of the contacts and 3| as the result of a decrease in pressure as previously described, will cause an increase in excitation of the generator it until these contacts again separate as a result of the as pressure having returned to normal. The result will be a periodic variation of pressure on both sides of normal which will be accentuated by the time constants of the field winding of the generator and of the motor. However, with the anti-hunting means such a variation is prevented, for as the contact 30 moves in response to pressure, the anti-hunting contact II is actuated to prevent the increase or decrease in excitation of the generator I! from lasting so long as to cause a material variation, so that the pressure with which the logs are urged against the grindstone remains substantially constant with a consequent greater uniformity of wood pulp.

The vibratory action of the anti-hunting means being responsive to the generator voltage and not to the field current of the machine, acts so rapidly that due to the time lag of the field winding of the geuerator, the current therein is held substantially constant, so that no periodic eifect 66 on the pressure is produced by this anti-hunting means. Our invention is not limited to the particular operating means for the anti-hunting contact which has been shown, and it will occur to those skilled in the art that many other ways 60 of securing vibratory action of the contact Il may be employed without departing from our invention in its broader aspect.

If the pressure is not increased by the regulating action which we have just described and the pressure exerted by the wood against the grindstone continues to diminish, the contacts 29 and H are closed after such pressure has diminished a predetermined amount. Assuming that a. jam has formed between the feed chains II and I2, 70 it will be apparent that the load current of the motor It will remain quite high, the result being that the coils II and 45 connected in opposition neutralize each other so that the spring I provided on the relay l2 closes the contacts of the relay. An energizing circuit for'the relay-4.8 is thereby completed which circuit may be traced from the supply line 24, conductor 88, contacts 28 and 4|, conductor I8, relay 42, conductor 11, through the contacts 18 shunted by the armature 18 of the relay 48, through the operating coil 88 and by conductor 8I to the supply line 28. The coil 88 thereupon causes the plunger to strike the lower portion of the armature I8 to move it from its normal position as shown by the broken line outline to the full line position. The operating coil 88 of the reversing switch II is thereupon energized through a circuit which may be traced from the supply line 28, conductor 82, the upper pair of contacts 88 on the relay 48, conductor 84, operating coil 85, conductors 88 and 81, the lefthand contacts 88 of the timing means 41, and by conductors 88 and 88 to the other supply line 24,

The reversing switch 2| thereupon closes to reverse the magnetism and voltage of the generator l8 causing a reversal in the direction of rotation of the motor I8 and consequently causing the chains II and I! to be driven in a direction to remove the pressure from the grindstone II or in the case a jam is formed, to break the jam.

When the reversing switch 2i was operated to its new position a switch 88 actuated with switch 2| was closed, establishing an energizing circuit for the timing means 41. This circuit may be traced from the supply line 23, contacts 88, conductor 84, switch-88, conductor 8|, a resistance 83, the coil 84, thence by conductor 88 and conductor 58 to the other supply line 24. It will be observed that the energization of the coil 84 exerts a force on the armature 85 of switches 88 and 88, tending to move the armature in a direction to open the switch 88 and close the switch 88. This movement of the armature 85, however, is prevented by a gravity operated latch 81. The energization of the timing motor 82, which is connected in parallel circuit relation, as shown, with the coil 84 and the resistance 88, causes its armature to be rotated, and by means of the worm gear 88, carried by the armature shaft, engaging a gear I88, serves to rotate the gear I88 in a. clockwise direction so that the projection I8I strikes the outer end of the catch 81 in a direction to release the armature 85, whereupon the armature is moved by the attractive effort of the coil 84. The skitch 88 is at the same time opened to break the circuit through the operating coil 85 of the reversing switch 2I, and the reversing switch 2| is thereupon operated to its original position. The closing of the switch 88 establishes an energizing circuit for the coil I82 of the relay 46, which circuit may be traced from the supply line 28, coil I82, contacts I88 shunted by the armature of the relay 48, by conductor I84, the switch 86 and thence by conductors 88 and 58 to the other supply line 24. The coil I82 thereupon operates the relay 48 to its original position.

It will of course be obvious to those skilled in the art, that as soon as the reversing switch 2| was returned to its former position, the generator voltage again reversed its polarity causing the motor l8 to drive the feed chains II and I2 in a direction to again feed the wood downwardly against the grindstone i1.

It will be remembered that the contacts of the relay 42 were closed because the coils 44 and 45 neutralized each other. The reversal of the motor III, as we have explained, serves to break the Jam of the logs which occurs between the feed chains. As soon as the jam is broken, the motor current becomes relatively small and consequently the opposition oflered by the coil 44 to the coil 48 becomes much less. The result is that the voltage responsive coil 48 opens the contacts of a the relay 42. We provide a dashpot I88 on the relay 42 so that this relay may only be closed after the occurrence of an interval of time. This interval of time is important in order to prevent an immediate reversal of the generator voltage after the direction switch 2| has been operated to its first position.

If, however, the Jam has not broken and the pressure remains below the predetermined amount on the grindstone II, it will of course be 18 understood that the contacts of the relay 42 again close, establishing the circuits as we have described them, causing the generator voltage to again reverse, hence reversing the drive of the feed chains II and I2.

The provision of the relay 42 causes our control system to discriminate between a condition of decreased pressure against the grindstone I! with a corresponding decrease of motor current and the condition of a jam where the motor cur- 85 rent is increased.

While we have shown a particular embodiment of our invention, it will be understood, of course, that we do not wish to be limited thereto since many modifications may be made, and we there- 30 fore contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. In a wood grinder, the combination of a grindstone provided with a shaft and bearings therefor, means for feeding wood against the stone to exert a pressure thereon, driving means for said feeding means, a pair of associated contacts, means for moving one of. said contacts in response to an output characteristic of said driving means, pivoted means supporting said other contact on one side of its pivot for movement toward and away from said other contact, means responsive to the bearing pressure of said grindstone for actuating said pivoted means, control means operable by said contacts to control the speed of said feed driving means, a second pair of contacts one of which is supported on the opposite side of said pivot for engagment with the other contact upon a predetermined reduction in said bearing pressure, and reversing means operable upon engagement of said second pair 55 of contacts for reversing said feeding means.

2. The combination with a grinding machine provided with a rotatable grindstone and feeding means for the grindstone, of a motor for driving said feeding means, a generator connected in 50 local circuit with said motor and provided with a field winding, a regulating resistance connected in circuit with said field winding for controlling said motor; a pair of contacts, means mounting said contacts for their mutual approach and 55 separation, connections for connecting said contacts to control said regulating resistance, means for operating one of said contacts in response to the bearing pressure of said grindstone and means for operating the other of said contacts 70 in response to the voltage of said generator.

3. The combination with a machine having a load supporting member, feeding means associated with said member, of a motor for driving said feeding means,- a supply generator provided with a field winding for controlling said motor, a pair of contacts, connections for connecting said contacts to control the energization of said field winding, means for moving one of said contacts in response to the bearing pressure of said member, and means for moving the other of said contacts in response to a generator electrical condition which varies with the output of said generator so that said contacts by their mutual approach and separation control said generator and said motor to maintain substantially constant the load on said supporting member.

4. In a wood grinder, the combination of a grindstone, its gearing, shaft and bearings, means for feeding wood against the stone to exert pressure thereon, driving means for said feeding means, a oil film between the shaft and its bearings subject to said pressure, a pair of contacts, means mounting said contacts for mutual approach and separation, connections for connecting said contacts to control said feed driving means, means for moving one of said contacts in response to an output characteristic of said driving means, and means for moving the other of said contacts in response to the pressure of said oil film.

5. In a wood grinding machine, the combination of a grindstone, its gearing, shaft, and bearings, means for feeding the wood against the stone to exert pressure thereon, an oil film between the shaft and its bearing subject to said pressure, a movable circuit regulating element operable in accordance with the pressure of said oil film, an electric means for controlling said wood feeding means, said electric means including an electric circuit the voltage of which is regulated by said movable element, and means for modifying the operation of said movable element in' response to the voltage of said electric circuit to prevent overregulation of said electric 5 means.

8. A control system for pulp grinding machines and the like, comprising a member for carrying out a predetermined operation upon the material, means for feeding said material to said ma- 1o chine so that a pressure is applied to said member, a motor for driving said feeding means, a source of electrical energy for supplying said motor, control means responsive to the pressure applied to said member for increasing said elec- 1s trical energy applied to said motor upon a predetermined 'd'ecrease of member, and means trol means responsive to the voltage of said source for modifying the action of said means go to prevent overregulation.

7. A control system for grinding machines for the production of wood pulp comprising a grindstone, feeding means for urging the wood against said grindstone, driving means for said feeding :5 means, means responsive to the bearing pressure of said grindstone and operatively associated with said driving means for controling its speed to maintain said bearing pressure substantially constant, and means responsive to speed variaso tions of said driving means for modifying the action of said pressure responsive means to prevent overregulation of said bearing pressure.

FRANK A. BYLES. FRED H. WINTER. 85

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