US2085128A - Paper dryness control - Google Patents

Description

, June 29, 1937.

S. A. STAEGE PAPER DRYNES S CONTROL Filed May 26, 1934 2 Sheets-Sheet 1 INVENTOR 5'7ephehi5faege.

ATTORNEY WITNESSES.

June 29, 1937.

S. A. STAEGE PAPER DRYNESS CONTROL Filed May 26, 1934 2 Sheets-Sheet 2 INVENTOR ffep/ver; flSfaeye.

WITNESSES: fi7%% 6! a. W

AT-TORNEY Patented June 29, 1937 UNITMIIZDSTATES 2,085,128 PATENT o FicE- 2,085,128 v PAPER nmmsss CONTROL Stephen A. Staege, Pittsburgh, Pa... assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application May 26, 1934, serial Nb. 727,748 v r r '6 Claims. '(01. 34-48) I I This 'invention relates to control systems for motors, and more particularly to systems of control wherein a motor governing the operation of a material drier is controlled in response .to the I 5 degree'of dryness ofthe material being dried.-

In the art of making paper the dryingoperation is an important feature and, to properly control the drying before the paper passes to the first calender, some means should be provided for 10 controlling the admission of steam to the drier. .OneobJect of my invention is to measure-the dryness of paper,.preierably between the drier and the first calender or in somecases at another location within the drier, and to control the dry- 15 ing operation by the measured dryness.

Another object of my invention is to control the drying rate in a paper drier as a function of the dryness of the paper leaving the drier but wherein the corrective action is effected in small 2 increments to thus prevent hunting. j

A furtherobject of my invention is to measure the dryness of paper or other material by means oiadrag element engaging the material, which element controls electric discharge devices which,

25 in turn, control a motor for changing the drying rate of the material.

A further object of my invention is to measure and control the drying rate of a drier for material as a function of the tension in the material 30 withvariations in moisture therein.

Other objects and advantages of my invention,

not specifically recited hereinbefore, will become apparent from a study of the follcwing specification,'when considered in conjunction with the ac- 85' companying drawings, in which:

Figure 1 is'a diagrammatic view showing a I drier, acalender and a system of control, for

controlling the operation of the drier; and

. I Fig. 2 is a modification showing elements simi- 40 larto those shown in Fig. 1. v a g Referringmore particularly to Fig. 1, I have shown therein a calender l -and the drums 2 of a drier formaterial passing through the drier .to the calender. ,The drums'2 are merely two of 45 a large number of drums included in a drier, all

of which are supplied with steam or some other hotjfluid for effecting a. drying operation of the paper 11 other material that may pass through the drier. ,1 show but two drums because two are suflicient-to illustrate the novel features of my invention.

A valve 3 .is provided for'controlling the rate.

or admission of the steam to the drums 2 from a supply pipe 4. .The position of this valve is controlledby a motor 5 operating the valve 3 through 'a worm 6-, worm wheel 1 and threaded valve stein 8. The motor 5, is of the reversing type and is-controlled in its-direction of operation by a dryness-measuring device 9,-which, in

60 turn, controls a pair of electric discharge devices discharge device becomes conducting the motor .5-

operates in one direction and when the other tube becomes conducting the. motor operates in the reverse direction. a g

The dryness measuring andcontrolling device 9 v includes a drag member l3 controlling the re- 10 actanceof a reactor l4. The reactor l4 has ,a magnetic circuit including a stationary member l5 and a movablefnember Hi, the position of which is determined by the adjustment of spring. .l'l through adjusting means l8 (co-operating nut and screw, for example) and the dryness of the material l2.- The dryness of 'the material l2 varies the coeflicient of friction, and in consequence, the member l3 will variably drag over the material i2 responsive to suchvariations in, the coefficient of friction. When the friction in- .creases armature I6 is moved toward the right, increasing the air gap in the magnetic circuit of the reactor l4 and thus changing the reactance value of this reactor. At the same instant, the 'dryness is indicated by the pointer l9 on the scale 20.

A pipe 2i is connected in the pipe leading fromthe valve 3 to the drums 2, to permit the steam pressure to enter the. region 23 of the chamber 22 to thus control the position of diaphragm 24 K with variations in the steam pressure in the drier drums 2. The diaphragm 24 is provided witha piston 25 operatingin a cylinder 26. v

The cylinder 26 is connected to a lever 21 pivoted at 28, and adjusted to a given position by the adjustable spring assemblies 29 and 30. With variations in pressure in the drier drums 2, the

' position of lever 21 is changed and, in consequence, he air gap for reactor 34 is changed by reasonof the fact that the movable armature 3| is shifted with reference to the stationary portion of the magnetic circuit 32 of the reactor 34.

A transformer 35 is provided to supply the required energy for motor 5 and the electric discharge devices Ill and II, and the circuits'i'or the respective reactors l4 and 34. The transformer 35 is provided with a secondary winding 35.101 energizing the reactors. I4 and 34, which reactors are connected in a Wheatstone bridge arrangement in such manner that one-half of the secondary winding-36 and one reactor constitute one leg of the bridge, whereas the other half of the transformer and the ptherreactor constitute the other leg of the bridge. A primary winding 31 is connected in the potentiometer circuit of this Wheatstone bridge arrangement a nd, as

is well known for this typ of circuit, any 11n- -balance in the reactance between the reactors l4 and 34 will cause a current to flow in thepria) mary winding 31, thereby inducing a current in the secondary windings 35 and 35 01' the grid control circuit 45.

The grid control circuit i. e. the phase-shift 5 grid biasing circuit 45 includes a secondary winding 4|, a capacitor 42 and a resistor 43. The upper terminals of the respective secondary windings 35 and 35 are connected to a junction 44 intermediate the capacitor 42 and the resistor 43.

m The other terminal of secondary winding 38 is connected to the grid 45 of the electric discharge device It through a resistor 46 whereas the other terminal of the secondary winding 39 is connected to grid 41 oi the electric discharge device ll through a resistor 48.

The electrical characteristics of the phase shift grid biasing circuit 40 are so selected for normal operation that the bias of the respective grids 45 and 41 with reference to the anodes 55 and 52 of the electric discharge devices Ill and II, re-

spectively, is such that these discharge devices will be caused to break down or become conducting substantially at the end of each positive portion 01' an altemating-current wave. An unbalance in the Wheatstone bridge arrangement will thus cause either. the electric discharge device l0 or the device II, as the case may be, to break down earlier during an alternating-current wave and thus supply the motor 5 with suflicient energy to'operate to readjust the valve 3 and thus reestablish the balance between the reactors l4 and 34. This will become more apparent from a study of the sequence of operation given hereinafter.

The cathodes 49 and 5! are energized from a secondary winding 53, whereas the motor 5 is connected to be energized from the secondary winding 54 of the transformer 35.

Both of the electric discharge devices are provided with timing circuits so related to the grids of these devices and the motor field windings 55 and 55, respectively, that the motor will be caused to operate at a lower and lower speed until the necessary correction has been accomplished. when very nearly the necessary correction has been accomplished the speed or the motor will be sumciently slow so that over travel is prevented. No hunting can thus take place.

Assume that'the paper I! is moved from the drier over the guide or idling rollers 59 and 50 to the calender I, and that a given amount of steam is supplied to the drier. It for some reason, the dryness in the paper is not of the appropriate value, such improper dryness will influence the position 0! the drag block l3 oi the dryness-indicating device 8, and in consequence,

the movable armature l5 will be moved either.

toward or away from the stationary portion of the magnetic circuit of the reactor i4. If it be assumed that an insufiicient amount of steam was transmitted to the drier and that the paper is moving to the calender with an excessive amount of moisture therein, the 'coefllcient oi friction will rise. In consequence, the air gap for 5 the reactor l4 will be increased. This unbalancing or the Wheatstone bridge circuit causes a current to flow through primary winding 31 and,

since the secondary windings 35 and 33 are connected in the phase shiit'grid biasing circuit 40,'

during an earlier portion of the alternating current wave and thus become more conducting than the other discharge device. 1

For the assumption made, the bias of the grid 45 is changed, and in consequence, the electric discharge device It becomes conducting. An energizing circuit is thus established from the right-hand terminal or the secondary winding 54 through conductor 5i, armature 52, field winding 55, anode 50, cathode 43, the secondary winding 53 and conductor 53 to the left-hand terminal of the secondary winding 54.

It should be noted that the grid resistor 45 is connected in shunt relation to the field winding 55, and the instant current begins to flow in the ileld winding 55 the tendency would be to make the grid again less positive with reference to the anode and, thus reduce the speed of the motor or stop it slightly in advance of complete correction. However, to prevent such immediate nullification oi the operation set up by reason of the unbalance in the Wheatstone bridge arrangement, the capacitor 34 is provided in shunt relation to the resistor 45. A second capacitor is also provided to prevent a closed circuit from being established in shunt relation to the field winding 55, and in shunt relation to the resistor 45 through the resistor 55.

In view of the timed biasing eflect accom-.

plished by the capacitor 54 the motor 5 will op erate for a short interval of time until the capacitor 64 has become fully charged, whereupon the electric discharge devices will cease to operate. This operation of the motor will first be at a comparatively high speed and as the capacitor 54 becomes charged the tube ill will break down, that is, become conducting at successively later periods of the alternating-current wave. However, if the unbalance still obtains in the Wheatstone bridge arrangement, the electric discharge device ill will again become conducting after more current passes through the field winding 55.

Operation oi the motor 5, of course, changes the position of valve 3 and since it was assumed an insufilcient amount of steam was being admitted to the drums 2, .valve 3 will be moved upwardly, thus admitting more steam to the drums 2. With a wider opening of valve 3 the pressure in the region 23 of the chamber 22 rises and the diaphragm 24 is moved upwardly. As the diaphragm 24 moves upwardly the piston 25 moves the cylinder 25 upwardly, thereby increasing the air gap in the reactor 34 to reestablish the balance. The piston 25 is provided with leakage apertures so that lever 21, utter a time; again takes the balanced position. This permits successive corrections to take place. 'With the operation of the motor 5 the air gap for the reactor 34 becomes greater until a balance is again established between the reactance oi the reactors I4 and 34.

When an excessive amount of steam is admitted to the drum 2, the drag member or block l3 will be actuated toward the left by the spring i1, and in consequence, the airgap will decrease i'or the reactor i4. This will change the bias on grid 41 oi discharge device II and cause the motor 5 to operate in a reverse direction. It is, or course, understood that for the reverse op- I eration capacitors 55 and 55 and resistor 15 have the same function as capacitors 54 and 55 and resistor 55, utilized in connection with the discharge .device III.

In the modification shown in Fig. 2, the ten-.

sionoithemateria-Lbeingameasureotthedryaccuse ness thereof, is utilized to indicate and control the dryness oi the material, The movable armature I6 01' the reactor I] is mounted on a bellcrank lever and the armature I6 is held in a 5 given position of adjustment by a pair oi adjustable springs 12 and 13. The armature i6 is mounted on one arm of a bell-crank lever provided with theroller ll engaging the material unbalance occurs because ot a variation in the; dryness or the material, shuntfcircuits Iorthe v respective field windings 55 and 56 are provided,

20 whichcircuits include capacitors, resistors and a pair of rectifiers. The rectiflers are utilized to prevent the capacitors from discharging through the field windings.

An unbalance occurring in the Wheatstone bridge arrangement will cause the motor 5 to start. However, to prevent the bias 'of the grid of the particular vtubethat may be conducting from immediately changing to a stable condition, a. shunt circuit is-establlshed for the field winding that may be energized. If the field winding 55 is energized, this circuit may be traced through resistor 18, capacitor 19, rectifier ,80,

conductor 8|, resistor ll, conductor 82, capacitor 83 and resistor 8|. The temporary change of the 35 current in the resistor II, while .the rectiilers mentioned are being-charged, delays'the changing of the bias on the grid 45 and in consequence the discharge tube in continues to operate until 'the capacitors are charged, whereupon the operation of motor ceases.

It the proper balance has not been established on the reactors I4 and M, the motor may again start operating and this cycle is repeated until the required change in the admission of the effected for the material l2.

It .the unbalance is ma different sense than just discussed, it is, of course, apparent that the tube II will be operated in a manner similar to that just discussed'ior tube lll.

I claim as my invention: v

1. In asystem of control for a drier,- in com:- bination, a plurality of drying elements, a valve for controlling the rate of admission oi the drying medium to the. drier elements, a motor-tor oper-- ating said valve, an electric discharge device con-.

nected in circuit relation with the motor and adapted to directly energize said motor, a control grid for said electric discharge device, a timing electric discharge device prior'to" lapse of a definite interval of time after .its energization, and paper dryness indicatingimeans tor controlling the grid oi! the electric discharge device as a tunction-ot the dryness of the paper. a

in combination. a valve for controlling the rate of admission of thedrying mediumlto thedrier, x

a motor for operating the valve, 0, pair ot'electric discharge devices interconnected with said motor and adapted to energize the motor for forward steam is made so that the appropriate dryness is circuit for preventing the dejenergiz'ation oi the 2. In a system or control for a drying-machine,

and reverse operation, depending upon which or the electric discharge devices becomes energized, grids for said electric discharge devices, means for changing the bias of the grids, a Wheatstone bridge arrangement including a pair of reactors and a pair of secondary windings oi the transformer, and a potentiometer circuit, said means' forcontrolling the grids being interconnected with the potentiometer circuit 01' the-Wheatstone bridge arrangement, means for moving material to be dried through the drier, a friction member engaging the material and controlling the reactance of one of said reactors, and a pressureresponsive device interconnected with the drier.

and responsive to the pressure of the drying medium ins-the drier forcontrolling the reactance of the second reactor. Y 3. In a system of control for a drier, in com-' bination, meansfor moving material to be dried through the drier, a friction member engaging the material and controlled in its position by the dryness oi the material beingdried, an electrical reactor controlled by the friction means, a second electrical reactor responsive to the rate of admission of the drying medium to the drier, a valve for controlling the admission of drying medium to the drier, a motor for controlling said valve, and means responsive to the differential reflect of said reactors for controlling the operation ofsaid motor. a

. 4. In a system of control for a drier, in combination, means for moving material to be dried through the drier, a friction member engaging the material and controlled in its position by the dryness of the material being dried, an electrical reactor controlled by the friction means, a

second electrical reactor responsive to the rate "of admission of the drying medium to the drier, -a valve for controlling the admission of drying medium to the drier, a motor for controlling said valve, and means, responsive to the difl'erential effect of said reactors, for eflecting the operation oi. said motor in successive steps.

' 5.In a system of control for a drier, incombination, means for moving material to be dried through the drier, a tension member engaging the material and controlled in its position by the dryness of the material being dried, an electrical reactorcontrolled by the tension means, a secand electrical reactor responsive tothe rate of admission of the dryingmedium of the drier, a

J valve for controlling the admission of drying medium to the drier, a motor adapted to control the valve, and means responsive to the diflerential 'eflect of said reactors adapted to control the operation oi! said motor. n

6. In a system of control for a drier, in combination, means for moving material to be dried through the drier, a tension member engaging .the material-and controlled in its position by the dryness oi the material being dried, an electrical reactor controlled by. the tension means, a second'electrical reactor, responsive to' the rate of admission .of the drying'medium to the drier, a valvei'or controlling the admission of the dry- I ing medium to the drier, a motor adapted to.

control said valve. and means, responsive to the diflerentlal eiiect of saidreactors, tor electing the operation of said motors in'successive steps.

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