US3551752A - Digital efflux ratio controller - Google Patents

Description

United States Patent Inventors App]. No.

Filed Patented Assignee DIGITAL EFFLUX RATIO CONTROLLER Lambert H l r [56] References Cited i?! g G r M H ht OF UNITED STATES PATENTS 2; 3 3,206,641 9/1965 Leeson, Jr. et al 3,064,173 11/1962 Breen et a1 Sept. 28, 1967 Dec 29 I970 3,110,853 11/1963 Jones Avmm Manufacturing Inc 3,331,006 7/1967 Strand Cleveland Ohio 3,427,442 2/ 1 969 Sklaroff a corporation 01' Ohio Primary Examiner-J. D. M illcr Assistant Examiner-William J. Smith Attorney-Richard MacCutcheon ABSTRACT: Digital frequency differencing and control apparatus useful as a speed ratio controller has an outwardly adclamsa Drawmg Figs justable calibrator for one pulse train input, a digital subtrac- U.S. Cl 317/138, tor which subtracts the frequency of the output of the calibra- 235/151.1:317/6; 318/20.300,318/20.320, tor from the frequency of another pulse train input, an ad- 318/20.360 justable digital divider fed by the subtractor, adjustable dura- Int. Cl G061 15/46 tion circuits fed by the divider, and a pair of relays respective- Field ofSearch 317/ 138, ly fed by said circuits to be alternatively operative, thus to 147, 5, 6; 235/151.1; 324/78D, 79, 83FCE; 318/20.300, 20.310, 20.320, 20.370, 39, 312,

20.360 circuits adjustments.

|s 1 W a 34 I l2 EUL'QE'QI e, cu (f-f 1 f DIGITAL at A ANTI COINClDENCE l 2 A f2 33 u r b i'lotu (f; fbi E DWIDER A CD & gmcun- 1 23 24 20 1 :3 a: c: 35 RESET 1 Y CALIBRATION CIRCUITS "I -21 f f I I I f f2 40 PULSE PULSE RAT'O -DURATION DURATION SELECTOR i: cmcul'r cmcul'r 1 i I "e 1 L 1 DECREASE INCREASE ouTPuT OUTPUT maintain a speed ratio as predetermined at the calibrator and at a proportional rate predetermined by divider and duration PATENTEU DECZS I970 MOE IVE

' BY )fikAmJ Wactifom ATTORNEY.

DIGITAL EFFLUX RATIO CONTROLLER CROSS REFERENCE TO RELATED APPLICATIONS In copending application of L. Haner and F. D. Sarver, Ser. No. 655,171, filed July 21, 1967, now Pat. No. 3,534,261

, there is disclosed a frequency differencing apparatus where such things as paper mill pulp feed slice velocity and supporting wire mesh travel speed are expressed as two pulse frequencies. According to that application, the incoming signals are taken first through anticoincidence circuitry and then through adigital subtractor to provide differential frequencies later converted to an output voltage representative of any frequency difference.

BACKGROUND OF THE INVENTION The present invention relates to measurement and control of sample material speeds and more particularly to maintaining a predetermined. ratio of speeds from point to point. l-leretofore, frequencydifferencing, for example as used to determine draw in a paper mill (as explained in the copending application) has been used to provide a readout of a voltage which is analagous to any difference in given input frequencies, thus useful for manual control of draw (tension) or its opposite (buildup). However, the prior analogue voltage "readout, and the prior equipment for producing it, have not been well suited for providing automatic control (a go" no-go" sort of thing) particularly because an automatic control preferably permits many more adjustments than does a control which is effected manually.

An object of the present invention is to provide relatively simple means for overcoming the above-mentioned difficulty.

7 SUMMARY OF THE DISCLOSURE According to one aspect of the present invention, a machine operator is relieved fr om making periodic adjustments on a semiliquid pulp feed valve in order to maintain proper relationshipbetween'pulp feed and process speed of resultant paper. As'mentioned in the foregoing Abstract this involves an outwardly adjustable calibrator, an adjustable subtractor, a

divider, a pair of adjustable duration circuits, and a pair of relays. Since one input frequency might, during use, be either greater than or less than the other, a useful adjunct is a polarity logic'circuit fed by the subtractor and active to gate the respective duration circuits, when the conditions as shown on FIG. 1 are true, in order topredetermine which relay shall be activated to afford correction.

DESCRIPTION OF THE DRAWING DESCRIPTION OF PREFERRED EMBODIMENT Referring first to FIG. I, and as mentioned in the copending application, in a paper mill, a head box level ofsemiliquid pulp 10 is conveniently measured by a pressure-to-frequency trans ducer 11, providing a frequency f, representative of so-called slice velocity as the pulp discharges out of a sluice onto a motorized wire mesh 12 whose speed is measured by a pulse generator tachometer 13 providing an output pulse per increment of process travel as a strip of paper I is formed. Two frequencies f, and f are thus provided.-

In illustrating the present invention, it is assumed pulp is supplied through a pipe section 14, then through a throttle valve 15 to the head box 16. Valve 15 is positioned by a servo device, such as an air or electric motor, 17, all of which might be existing equipment with the direction of the valve motor controlled by pushbuttons (not shown) in order to either increase or decrease the flow of-material into the head box. The output from the digital effluxr'atio controller of the invention, about to be described, can either replace or be tied in parallel with any such existing increase and decrease pushbuttons, as desired.

In the digital efflux (output) ratiocontroller itself, the pulse signals f (whose frequency is proportional't'o slice velocity) and f (whose frequency is proportibfia l t'o 'wire mesh speed) are suitably conditioned as by 3111pI1fi8 FS'19,20, As illustrated, the output of amplifier 19 is taken to'calibrator and ratio selector circuits as indicated by the block 21.

In FIG. 1, the calibrator and ratio selectors pulse train out put, for convenience also called f (because it is 'still proportional to slice velocity) is taken to a digital subtractor apparatus-22 in which it is compared (differenced) with respect to the amplified f output of tachometer 13. This provides three modes of'subtractor output:'( 1) zero (f, =f (2) a socalled count up condition assumed when f, is greater than f or (3) a count down" condition (f, less than f The alternative CU and CD outputs are taken to a NOR gate 23, because, for counting the difference frequency Af, a subsequent digital divider 24 cares not whether the count is up or down.

The digital divider provides an output, Af/A, and to make it suitable for electromechanical relay operation this output is taken to a pair of pulse duration circuits 25, 26 respectively arranged for alternatively operating relays 27 (for decreasing flow through the throttle valve 15) and 28 (for increasing the flow), according to information from a polarity circuit 29 which indicates whether the count e.g., offl) is too high or too low.

For the pressure-to-frequency transducer 11, standard ap paratus can be used e.g., a differential pressure cell producing a DC signal proportional to voltage plus an electronic package for converting the voltage to a proportional frequency).

For the calibrator and ratio selector 21, standard, well known circuits may be used. See Computer Handbook, by Huskey & Korn (McGraw-Hill, 1962), Page 2l90',- and while flip-flops might be used (to give /2, A, /a, etc), we prefer the use of decades (e.g., giving .l, X1, X 10, X 100), and we prefer to use just one counter (fine to coarse decades, each of which runs up to 9 and then gives a signal to the .next in line) with what might be thought of as two manual calibrators, one being a set of thumbwheel or rotary switches 31 normally hidden within the equipment, as indicated by the dashed lines, (for start up calibration, as for .tachometer characteristics, etc.), and the other being a set of three rotary switches located on the front of a housing or on a front panel 32 exteriorly of the box (not shown) in which the predominance of the electrical equipment is normally enclosed.

Since the operation of the whole unit is to continuously I measure and monitor frequency proportional to slice velocity (e.g., proportional to square root of head box pressure) with respect to frequency proportional to mesh wire speed, and then deliver a contact closure output in accordance with deviation from an established ratio, thus to adjust percent of draw (pull of paper P) or, alternatively, adjust percent of buildup (of pulp on mesh behind paper P), the switches on panel 32, for inserting a desired ratio into the calibrator, provide a readily accessible selection of ratio between slice velocity and wire mesh speed, e.g. from 90.0 percent to 109.9 percent, an adjustment which provides a resolution of l/lO of 1 percent with good accuracy (once the internal manual switches 31 have properly compensated for proportionality constants relating slice velocity frequency .to actual slice velocity and wire speed frequency to actual wire speed).

For performing the arithmetical operation of subtracting one input frequency from the other (as calibrated) we prefer a digital subtractor which is preceded by anticoincidence circuitry suitably clocked by frequency supplied by an oscillator 33. For the anticoincidence and digital subtraction circuit 22), suitable circuitry is shown in FIGS. 3 and 4 of the abovementioned copending application of Haner and Sarver.

The digital divider 24 is in essence a preset counter which may, and as assumed at 34 does, have a preset adjustment from I to 999. The divider counts the pulses at frequency Af up to the preset point at which time it delivers an output signal to both pulse duration circuits and also an output signal to a reset circuit 35, which may simply be a one-shot multivibrator. This automatically resets the digital divider 24 to zero.

The polarity circuit 29 may comprise a bistable multivibrator (flip-flop) which, as indicated at 29' in FIG. 2, is triggered by either the CU or the CD output of the subtractor 22 to change pulses to a steady signal down* or a steady signal "up" not only for enabling the respective pulse duration circuits, but also, as through an OR gate 36 (FIG. 2) and a wire junction OR 37 (FIGS. 1 and 2), resetting the divider 24 whenever one of these steady signals starts.

For each of the pulse duration circuits 25, 26, suitable circuitry may, as shown in FIG. 3, comprise an AND 38, a one shot 39 having a relay (27 or 28) closed time adjustment symbolically shown at 40, and an amplifier 41.

SUMMARY OF OPERATION In operation, let it be assumed that the frequency f is 1,000 c.p.s. and the frequency f,, as calibrated, is 1,005 c.p.s. The difference between these two frequencies is 5 c.p.s. and corresponds to a magnitude of 1/2 of 1,percent of frequency f The output frequency Af would then be equal to the difference of 5 c.p.s. Since frequency f, is greater than f then the corresponding output wire from the polarity circuit is active which means that relay 27 is enabled for control operation. Assume that the preset on the digital divider circuit is set at 100. If the digital divider circuit starts from the condition, it would take I00 pulses on the input in order to reach the preset level. It can be seen with an input pulse rate of p.p.s., it would take seconds before the preset level would be reached. For as long as the difference frequency is 5 e.p.s., every 20 seconds there would be an output control action from the controller. If the digital divider preset were adjusted to 20, for example, we can see that the frequency of output correction would be one every 4 seconds for the same magnitude of error or frequency difference. Also, if the preset on the digital divider were adjusted to 500, it would take 100 seconds between each corrective action delivered from the controller. It can be seen from the numerical example cited that the frequency with which the control action is given'is proportional to the magnitude of the error as well as to the preset number set into the digital divider. The digital divider therefore is a means for adjusting the controller loop gain. This feature allows great flexibility in establishing how fast or how slow the controller will respond to an error signal, and cooperates with the other adjustments; calibration interval (31, for calibration), calibration external" (32, for ratio selection), and pulse duration (40 or 40, for adjusting the duration of time for which either relay contact is closed, e.g. from a fraction of a second to several seconds) in order to easily arrive at both corrections and correction rates which are compatible with the desired response of the total system.

There is thus provided apparatus of the class described capable of meeting the objects above set forth.

While we have illustrated and described a particular embodiment, various modifications may obviously be made without departing from the true spirit and scope of the invention intended to be defined only by the accompanying claims taken with all reasonable equivalents.

We claim:

1. Digital apparatus for ratio control in a process for treating a sample material, said apparatus comprising:

a first source of pulses whose frequency is proportional to a mechanical condition in one portion of said process;

a second source of pulses the frequency of which is proporpulses from the digital subtractor circuitry;

at least one pulse duration circuit fed from the output of the digital divider and enabled by the polarity signal output of the digital subtractor circuitry and providing a time proportioned output; and

means fed by the electrical output of said pulse duration circuit and for varying one of said mechanical conditions and thus the frequency of one of said sources of pulses.

2. Digital apparatus as in claim 1 further characterized by a calibrator and ratio selector interposed between the digital subtractor and one of said first and second sources of pulses, said calibrator and ratio selector having:

a counter;

relatively inaccessible manual adjustment means for feeding calibration to said counter; and

relatively accessible manual adjustment means for feeding ratio selection to said counter.

3. Digital apparatus as in claim 2 further characterized by:

the digital division performed by the digital divider being adjustable; and

the pulse duration time achieved by the pulse duration circuit being adjustable, whereby corrections, correction magnitudes and correction rates are all adjustable.

4. Digital apparatus for ratio control in a process for treating a sample material, said apparatus comprising:

a first source of pulses whose frequency is proportional to a mechanical condition in one portion of said process;

a second source of pulses whose frequency is proportional to a mechanical condition in a disparate portion of said process;

a digital subtractor fed proportional to frequencies of said first and second sources and providing an output which represents the difference, if any, between the pulse frequencies, the digital subtractor having a first output mode when the frequency of its input which is proportional to first source frequency exceeds that of the input which is proportional to second source frequency, and having a second output mode when the opposite is true;

a calibrator and ratio selector interposed between the digital subtractor and one of said first and second sources of pulses, said calibrator and ratio selector having a counter, relatively inaccessible manual adjustment means for feeding calibration to said counter, and relatively accessible manual adjustment means for feeding ratio selection to said counter;

a digital divider fed responsive to output from the digital subtractor;

a polarity circuit connected to the subtractor and having two outputs, one operative when the digital subtractor first output exists and the other operative when the digital subtractor second output mode exists;

at least one pulse duration circuit fed from output of the digital subtractor and providing a time proportioned electrical output;

and there being a pair of means for varying a mechanical condition, one of the pair gated by the polarity circuit through one of its outputs while connected to be fed by the digital divider and for varying one of the mechanical conditions and thus the frequency of one of said sources in one sense, and the other of the pair gated by the output of the polarity circuit and connected to be fed by the digital divider and for varying the same mechanical condition, and thus the frequency of the same source of pul- 565, in an opposite sense.

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