US2338503A - Control system for paper machines - Google Patents

Description

Jan. 4,,1944. w. H. FORMHALS 2,338,503

CONTROL SYSTEM FOR PAPER MACHINES Filed Jan. 2, 1943 Patented Jam 4,1944

CONTROL SYSTEM FOR PAPER MACHINES William H. Formhals, Forest Hills, Pa., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application lanuaryz 1943, Serial No. 471,143

10 Claims.

This invention relates to a control system, and more particularly to an improved arrangement of a control system in paper making apparatus for preventing sag back upon breakage of the paper between the last set of drier rolls and the calender rolls, or similar applications.

In some forms of paper making apparatus, the paper is maintained under tension between the last set of drier rolls and the calender rolls. In so doing, the motor driving the calender rolls is'caused to take up part of the load necessary to drive the last set of drier rolls. In other words, a part or more of the power than is necessary to drive the last set of drier rolls is furnished by the drive for the calender rolls,

the amount of power being thus furnished being dependent upon the amount oi tension in the strip of paper between the drier rolls and the calender rolls. In such apparatus the drier rolls and calender rolls are connected to direct-current machines, and where power is being supplied to the drier rolls from the calender rolls through tensioning of the paper, the direct current machine connected to the drier rolls will supply only a portion of the power or be overhauled and operated as a generator.

In such case, ity is necessary to strengthen the field on the direct current machine connected to the drier rolls in order to maintain the other than the drive for the calender rolls if "sag back" is tobe prevented. This is accomplished by weakening the field on the direct' currentmachine connected to the drier rolls' in such manner as to cause it to take up the load on the drier rolls. However, electrical paper'mill drives thus far have been found defective in that the regulating apparatus for termined speed, this time delay or sluggishness of speed regulating systems heretofore available resulted in a slowing down of the last drier roll set and the formation of a loop or sag back" 'of the paper being fed to the last drier: roll set. The "sag back" oi the paper results in the formation of wrinkles and creases in the paper as it is subsequently fed through the last drier roll set. Such wrinklesare effective not only to deteriorate the;paper being made, but also result in weakening the same with further breakage between the calender rolls and drier rolls after subsequent rethread- 'ing of the paper through the calender rolls.

One of theprincipalobjects of this invention is to provide an improved arrangement of control apparatus for paper mill equipment which will be effective to prevent the so-called sag back of paper in front of the last drier roll set in the event of breakage of the paper in front of the calender roll set.

A further object of this invention is to pro- 'vide generator means intermediate the direct current drive motor for the calender rolls and a dynamo connected to the last set of drier rolls which is responsive to the operating conditions of the calender drive motor for eiiecting proper regulation of the drier roll dynamo with a minimum of time delay.

A further object of this invention is to provide a constant speed generator between the direct current machines connected to the cal-v ender and drier roll sets of paper mill equipment, together with means for rendering 'the output of each generator responsive to the operating conditions of the calender drivemotor description taken in connection with the accontrolling the speed of operation or the varv ious roll setsrequired a certain amount of time to change the characteristics of the direct current machine connected to the drier rolls in such manner as to cause it to take up the load on the drier rolls in the event of breakage of'the paper between the drier and calender roll sets. Since the paper is delivered companying drawing, in which:

Figure 1 is a diagrammatic showing of paper 'mill equipment having a speed regulating control system constructed in accordance with V the principles of this invention; and

Fig. 2 is a partial view of a part of the con- .trol apparatus shown in Fig. 1 showing a rectifier for controlling the direction of current flow in the armature circuit of the speed regulating generator.

Referring to the drawing, the numeral l desto the last drier roll set at a constant predeignates, as a whole, the last set of drier rolls and the numeral 2 designates, as a whole, a set of calender rolls. A strip of paper 3 is shown reeled around the rolls of a drierroll set and threaded throughthe-stack of rolls in the calender roll set. A dynamo 4 is shown mechanically connected to the drier roll set, and a motor 5 is provided for driving the calender roll set 2. The paper is fed to the drier roll set I at a constant rate of speed from roll sets (not shown) preceding the drier roll setgi in a manner customary in apparatus of this kind. As pointed out above',the paper 3 intermediate the roll sets I and 2 iscommonly maintained under tension and motor 5 is thus effective to provide part of, all of, or more than, the power for operating the drier roll set I. In case the motor 5 supplies more power than necessary to the drive roll.

set I, generator machine 4 operates as a braking on the drier rolls. The parts thus far described, including the mechanical connections of the direct current machines 4 and 5 to, and the mountings of, the roll sets I and 2 form no part per se of this invention, this invention being limited to the control apparatus for the direct current machines 4 and 5. It willbe understood that such control apparatus is used in connection with the conventional speed regulating devices (not shown) normally employed for matching the speeds of the various roll sets.

With respect to the novel features of this invention, the strip of paper 3 intermediate the roll sets i and 2 may be regarded as a, coupling means by which power is delivered from the calender roll set 2 to the drier roll set i.

The operation of the dynamo 4 is controlled by the direct current motor 5 through a generator 6 driven by a constant speed alternating current'mach ine 'I. 'The output of the generator 6 is controlled by means of a field 8 connected in series with the armature circuit of the motor 5, a shunting resistor 9 being provided for limiting the amount of current fiow through the field 8. The field 8 is arranged in bucking relation to a field Ill connected to a constant source of potential suchas the buses ii and I2.

A control field 13 for the dynamo 4 is connected in series with the armature circuit of a generator 6. The remainder of the excitation for the dynamo 4 is provided by a field I4 connected to the constant potential buses II and I2. Excitation for the motor 5 is provided by a field I5 likewise connected to the buses II and I2. The armatures of the machines 4 and 5 are connected to a source of variable voltage supply such as the buses I6 and I! to which the armatures of the other drive motors (not shown) for the remainder of the paper mill equipment (not shown) are also connected.

The remainder of the control apparatus shown in Figll comprises variable resistors I8, I9 and 20, respectively connected in the circuits of the dynamo field I4, generator field I0, and motor field I5, together with variable resistors 2I and 22 respectively connected in'the circuits of the variable control field I3 and the variable generator field 8.

The number of ampere turns in the generator field III is selected to be normally greater than the number in the variable generator field 8;

Since it will be recalled that the variable field 8 is arranged to buck the constant field II), it will be apparent that the total field on, and thereby the outputof the generators B, will decrease as the load taken by the motor 5 increases. As the load taken by the motor 5 increases, its armature will draw increased current and the field 8 will increase proportionally to the current drawn by, or the load taken up by, the armature of the motor 5. In this manner, the output 01' the generator 5 will decrease proportionately to the load taken by the motor 5. The dynamo field I3 is arranged differentially with respect to the dynamo field I4, and it will thus be seen that the total field on the dynamo 4 will increase with the decrease in output of the control generator 6 and with the increased load taken by the armature 5. The variable control field I3 is so designed that itsdecreasing effect on the total field of the dynamo '4 will change the field characteristics of the dynamo 4 in integrated steps from that of a motor to that of a generator without speed variations of the drier rolls as the motor 5 functions to relieve the dynamo 4 of the drier motor load. This regulation can be effected in such manner that the motor 5 through the paper 3 may take up either a portion of the power necessary to drive the drier roll set I, all of such power, or more than the power necessary. In the latter case, the dynamo 4 will function as a braking generator on the drier roll set I to dissipate the excess power being supplied thereto by the motor 5 through the coupling means provided by the tension of the paper 3.

A better understanding of the principles of this invention will be had by a consideration of the operation of the apparatus as paper is fed through the roll sets I and 2 and upon subsequent breakage of the paper intermediate such roll sets..

Operation of the apparatus is initiated by energizing the direct current buses II--I2 and I6II and initially no paper will be contained in the roll sets I and 2. The motor 'I will be operating and will function to supply maximum current to the control field I3, since the generator field 8 will be at a minimum due to the armature 5 drawing a minimum of current. The resistors i8, I9, 20 and 2! are adjusted to give the proper speed regulation of the roll sets I and 2. A strip of paper is then fed through the drier roll set I and thence through the calender roll set 2. As the paper is fed through the calender roll set 2, the load on the motor 5 will increase and a resultant increase in its armature current and the current flowing through the variable generator control field 8' will be had. Increase in the field 8 will decrease the output of the generator 6 and thus increase the total field on the dynamo 4, thereby causing the dynamo 4 to take up less of the drier roll load or to act as a braking generator according to the desired conditions of operation without interfering with the speed of operation of the roll set I.

With paper being fed through the roll sets I and 2 and the paper preceding the set 2 being under tension according to the above conditions, the condition which will be had upon snapping or breaking or the paper between the sets I and 2 will now be considered. Upon such breakage taking place, the motor 5 will cease to transmit power to the drier roll set I and the amount of current drawn by its armature will immediately drop to the value prior to feeding the paper through the stack of calender rolls 2. Such drop in armature current will likewise decrease the current flowing through the field 8 with a conwill decrease the field of the dynamo 4 and restore to such dynamo its original motor charactertistics causing it to act immediately to supply the power necessary to drive the drier roll set I without any change of speed. In this manner the characteristics of the dynamo l are changed immediately to compensate for the breakage of paper, and this is done with a minimum of time delay. The rapid change of operating characteristics of the dynamo 4 is efiective to maintain the speed of operation of the drier" roll set I without any slowing down which would otherwise be effective to cause a loop or sag back in the paper being fed to the drier roll set I.

The control generator fields 8 and III are so I regulated that under normal operating conditions of the roll sets I and 2 they will cancel each other, and the output of the generator 6 and value of the control field I3 will be zero. This usually represents the most desirable conditions of operation, but it is to be understood that the principles of this invention are equally applicable to other arrangements or adjustments of the various control fields in which the condition does not exist.

It will be seen that, under the desired conditions of tension operation, current will flow in the armature circuit of the generator Ii'in a single direction, and will vary from a maximum when the motor 5 is not transmitting power to the drier roll set I to a minimum when the load on the calender motor 5 and the tension in the paper 3 is at a maximum. To prevent the flow of current in the armature circuit other than in a single direction, a rectifier 23 of a type adapted to limit current fiow to a single direction may be inserted in the armature circuit of the generator Ii. The construction of the rectifier 23 forms no part per se of this invention, and accordingly has not been illustrated and described in detail, the construction and operation of such rectiflers being well known in the art.

From the foreging, it will be seen that the control apparatus of this invention enables the characteristics of the dynamo 4 to be changed automatically in accordancewith the load on the calender motor without any change of speed in op-' eration of the drier roll set. The load on the calender motor being a function of the tension in the paper, it will be seenthat the field of the dynamo 4 must be changed in accordance with such load as its operation changes from that of motoring tothat of generating if speed is to be maintained. By utilizing theai'mature current of the calender motor for regulating the generator 6 and thereby the field and operation of the dynamo 4, the necessary changes are made to prevent speed changes such as would cause sag back.

Since certain changes may be made in the above construction and different embodimentsof the invention may be made without departing from the scope thereof, it is intended that all the total field on said dynamo will impart motor characteristics thereto, a direct current motor for driving said calender rolls adapted to take up part of the load on said drier rolls by tensioning the paper between said -roll sets, and means responsive to loading of said calender drive motor for changing the output of said generator. means to thereby increase the field of said dynamo.

2, In paper making apparatus, a set of drier rolls to which a strip of paper is fed at a predetermined rate, a set of calender rolls to which said paper is fed from said drier rolls, a dynamo mechanically connectedto said drier rolls, a pair oi fields for said dynamo, a constant source of excitation for one of said fields, a variable source of excitation for the other of said fields, comprising a generator having a variable output, a direct current motor for driving said calender rolls,

and means responsive to the loading of said calender drive motor for varying the output of said generator in such manner that the field on said dynamo whenfsaid motor is unloaded will impart motor characteristics thereto, and when the loading of said motor is increased the field' of said dynamo will be increased so that said dynamo will take up less of the load and may be operated as a generator without speed changes.

3. In p'aper making apparatus, a' set of drier rolls to which a strip of paper is fed at a predetermined rate, a set of calender rolls to which said paper is fed from said drier rolls, a dynamo mechanically connected to' said drier rolls, a pair of fields for said dynamo, a constant source of excitation for one of said fields, a variable source of excitation for the other of said fields comprising a generator having. a variable output, a pair of fields for said generator, one of said gen- 7 erator fields having a constant source of excitamatter contained in the above description or shown in the accompanying drawing shall be I ior energizing one of said fields to an extent that interpreted as illustrative and not in a limiting tion, a direct current motor for driving said calender rolls, the other of saidgenerator fields being connected with the armature circuit of said calender drive motor in such manner that the total field on said dynamo will impart motor characteristics thereto for driving said drier rolls when said calender motor is unloaded and will increase the field on said dynamo as the load on said calender motor is increased.

4. In paper making-apparatus, a set. of drier' rolls to which a strip of paper is fed at a predetermined rate, a set of calender rolls to which said paper is fed from said drier rolls, a dynamo mechanically connected to said drier rolls, a direct current drive motor for driving said calender rolls adapted to transmit power to said drive rolls through said paper, and generator means for controlling the operation of said dynamo adapted to impart motor characteristics thereto when said drive motor isnot transmitting power to said drier rolls through said paper; and adapted to change'the characteristics of said dynamo to enable the same to take up less of the load of said drier rolls when said drive motor is transmitting power to said drier rolls through said paper. p

5 In paper making apparatus, a set of drier rolls to which a strip of paper is fed at a predetermined rate, a set of calender rolls to which.

said paper is fed from said drier rolls, a dynamo mechanically connected to said drier rolls, a

direct current drive motor for driving said cal- .ender rolls adapted to transmit power to said ing the output of istics thereto, and

6. In apparatus having a pair of machines for.

performing work, means coupling said machines together whereby the power for driving one of said machines may be supplied by the other or said machines, a dynamo mechanically connect.- ed to said one machine, a pair of fields for said dynamo, generator means for energizing one of said fields to an extent that the total field on said dynamo will impart motor characteristics thereto, a direct current motor for driving said other machine, and means responsive to loading of said other machine for changing the output of said generator means to thereby increase the field of said dynamo with the loading of said motor. I

7. In apparatus having a pair of machines for performing work, means coupling said machines together whereby the power for driving one of said machines may be supplied by the other of said machines, a dynamo mechanically connected to said one machine, a pair of fields for said dynamo, a constant source of excitation for'one of said fields, a variable source of excitation for the other of said fields comprising a generator having excitation for the other of said fields comprising a generator having a variable output, a pair of fields for said generator, one of said go'nerator fields having, a constant source of excitation, a direct current motor for driving said other machine, the votherofsaid generator fields being connected with the armature circuit of said drive motor in such manner that the total field on said dynamo. will impart motor characteristics thereto for driving said one machine when said other machine is not transmitting power thereto, and will increase field on said dynamo so that'it may take less load without change of speed when said to or change the characteristics of said dynamo a variable output, a direct current motor for driving said other machine, and means responsive to the loading of said drive motor for varysaid generator in such manner that the field on said dynamo when said drive motor is unloaded will impart motor characterwhen the loading of said motor is increased the field of said dynamo will be increased to enable saiddynamo to take less of the load of said one machine without interfering with the speed of operation thereof.

8. In apparatus having a .pair of machines for performing work, means coupling said machines together whereby the power for driving one of said machines may be supplied by the other of said machines, a dynamo mechanically connected to said one machine, a pair of fields for saiddynamo, a constant source of excitation for one of said fields, avariable source of so that it will supply less power without consequent speed variations when said coupling means is operating to transmit power from said other to said one machine.

10. In apparatus having a pair of machines for performingwork, means coupling said machines together whereby the power for driving one of said machines maybe supplied by the otherof said machines, a dynamo mechanically connected to said one machine, a direct current motor for driving said other machine, a constant speed generator for controlling the-operation of said dynamo, and means responsive to the operation of said motor for controlling the output of said generator, said last named means being effective to decrease'the field of said dynamo so that it willsupply less power when said coupling means is operating to transmit power to said one machine, and to impart motor characteristics to said dynamo for maintaining the speed of said one machine when said coupling means is imperative to transmit power to said one machine. a

' WILLIAM H. FORMHALS.

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