US3840025A

US3840025A - Tobacco moisture control system and method

Info

Publication number: US3840025A
Application number: US00280115A
Authority: US
Inventors: D Koenig; R Fowler; E Freeh
Original assignee: Industrial Nucleonics Corp
Current assignee: Industrial Nucleonics Corp; ABB Automation Inc
Priority date: 1972-08-14
Filing date: 1972-08-14
Publication date: 1974-10-08
Anticipated expiration: 1991-10-08
Also published as: GB1445198A; AU5921573A; JPS50105894A; CA999208A; DE2341100A1; ZA735415B

Abstract

The amount of moisture removed by a dryer from a stream of tobacco formed by mixing a supply of cut rolled stems with a supply of laminae is controlled. Gauge means respond to the cut rolled stems and laminae fed to the dryer to derive signals respectively indicative of the moisture of the cut rolled stems and laminae. The signals indicative of the cut rolled stems and laminae moisture are processed with a set point signal for the moisture of tobacco after emerging from the dryer to derive a feed forward component of a set point signal for the dryer drying rate. The cut rolled stem and laminae moisture indicating signals are processed differently from each other, as a function of the relative ability of the dryer to remove moisture from the cut rolled stems and laminae. A feed back component of the dryer drying rate set point signal is derived from a proportionalintegral controller responsive to the moisture indication of the dried tobacco.

Description

ited States Patent [191 Fowler et a1.

[ TOBACCO MOISTURE CONTROL SYSTEM AND METHOD [73] Assignee: Industrial Nucleonics Corporation, Columbus, Ohio [22] Filed: Aug. 14, 1972 [21] Appl. No.: 280,115

[52] US. Cl 131/135, 34/25, 34/52, 131/21 A [51] Int. Cl A241) 9/00 [58] Field of Search 131/135, 21 R, 21 A, 21 B, 131/21 C, 21 D, 140 P; 34/25, 52, 53

24 a CONTROLLER 6/1968 Wochnowski 131/135 7/1971 Wochnowski et a1. 131/21 A Primary Examiner-Wm. H. Grieb Attorney, Agent, or Firm-Allan M. Lowe [57] ABSTRACT The amount of moisture removed by a dryer from a stream of tobacco formed by mixing a supply of cut rolled stems with a supply of laminae is controlled. Gauge means respond to the cut rolled stems and 1aminae fed to the dryer to derive signals respectively indicative of the moisture of the cut rolled stems and laminae. The signals indicative of the cut rolled stems and laminae moisture are processed with a set point signal for the moisture of tobacco after emerging from the dryer to derive a feed forward component of a set point signal for the dryer drying rate. The cut rolled stem and laminae moisture indicating signals are processed differently from each other, as a function of the relative ability of the dryer to remove moisture from the cut rolled stems and laminae. A feed back component of the dryer drying rate set point signal is derived from a proportional-integral controller responsive to the moisture indication of the dried tobacco 17 Claims, 2 Drawing Figures [56] References Cited UNITED STATES PATENTS 2,768,629 10/1956 Maul 131/135 3,039,201 6/1962 Esenwein et a1.... 34/48 3,241,249 3/1966 Lavender 34/25 3,280,474 10/1966 Van Doorn et a1 34/31 3,372,488 3/1968 Koch et al. 34/46 7.7. 11 CUT ROLLED STEMS LNMNAE E PAIENIEDUBT 8M4 3.840.025

SBEEI 20F 2 b F/aZ COMPUTER TOBACCO MOISTURE CONTROL SYSTEM AND METHOD FIELD OF INVENTION The present invention relates generally to a system for controlling the drying rate of a tobacco dryer and, more particularly, to a system wherein the drying rate is controlled differently in response to moisture indications of cut rolled stems and laminae.

BACKGROUND OF THE INVENTION In the processing of tobacco, it is frequently the practice to strip laminae from stems, press or roll the cut stems, and mix the cut rolled stems with the laminae. The mixed, cut rolled. stems and laminae are supplied as a stream to a dryer desirably controlled so that conditioned tobacco after emgerging from the dryer should have a predetermined moisture.

It has been found, however, that the moisture of the tobacco after having been processed through the dryer, frequently deviates from the predetermined value. We have found that the deviation from the preset value in processes wherein the cut rolled stems and laminae are mixed frequently occurs because of the differential effects of the dryer on the cut rolled stems relative to the laminae. To our knowledge, there has been no recognition in the prior art of this differential effect and dryer control has been in response to the moisture of the mixture fed into the dryer.

SUMMARY OF THE INVENTION In accordance with the present invention, the moisture of the cut rolled stems and the laminae are separately determined and the dryer drying rate is controlled in response to these separate measurements. The invention can be utilized with tobacco dryers either of the rotary drum or fluidized types.

In a particular embodiment of the invention, dryer drying rate is controlled by determining the moisture weight per unit time of the laminae and cut rolled stems supplied to the dryer. A computer responds to the laminae and cut rolled stems moisture indications and a set point for the desired dried tobacco moisture to derive signals indicative of the amount of moisture expected to be removed by the dryer from the cut rolled stems and the laminae. The relative values of these signals are modified in accordance with the ability of the dryer to remove moisture from the cut rolled stems and laminae. The modified signals are linearly combined and effectively filtered to remove transient effects to provide a feed forward component for a set point for the dryer temperature. A feed back component for the dryer temperature set point is derived by providing a proportional-integral controller responsive to an indication of the actual moisture of the tobacco after being dried.

It is, accordingly, an object of the present invention to provide a new and improved system for and method of controlling a dryer responsive to a mixture of cut rolled stems and laminae.

Another object of the invention is to provide a system for and method of controlling the drying rate of a dryer so that the differential drying effects of the dryer on cut rolled stems and laminae are compensated.

The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of several specific embodiments thereof, especially when taken in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic diagram of one embodiment of the invention, wherein a rotary drum dryer is utilized; and

FIG. 2 is a schematic diagram of a second embodiment of the invention wherein a fluidized cycle dryer is utilized.

DETAILED DESCRIPTION OF THE DRAWING Reference is now made to FIG. 1 of the drawing wherein there are illustrated supply 11 of cut rolled stems and supply 12 of tobacco laminae which are obtained by cutting and separating the laminae from the stems of tobacco leaves. Both

supplies

11 and 12 have been previously processed so that the tobacco therein has been moistened to approximately 20 percent and thereafter cut. The moist, cut tobacco in supplies 1] and 12 is fed to belt

weigher conveyors

13 and 14, thence to conveyors l5 and 16, so that the supplies on

conveyors

15 and 16 are mixed and fed to dryer 17 via conveyor 18. In the embodiment of FIG. 1, dryer 17 is of the rotary drum type, whereby the resident time of the tobacco mixture therein is on the order of minutes. Tobacco emerging from dryer 17 is cooled with a stream of conditioned air, in cooler 19. Conditioned tobacco emerging from cooler 19 is fed to a storage facility 21 via conveyor 20.

Our investigations have indicated that dryer 17 does not remove each pound of moisture from the cut rolled stems at the same rate as each pound of moisturefrom the laminae. For one particular type of tobacco and one particular dryer installation, it was found that the amount of dryer effort required to dry one pound of laminae moisture to a desired specification was approximately one and one-third times the amount of dryer 1 effort required to bring one pound of cut rolled stem to the same moisture. In accordance with the present invention, the differential drying rate of dryer 17 on the moisture of the two

tobacco supplies

11 and 12 is determined to establish the drying rate of dryer 17 which is determined by a set point for the dryer temperature. To control the temperature of dryer 17, the dryer is responsive to a steam source 22 which functions as a heat exchange fluid affecting the dryer drying rate by supplying steam to the dryer through variable opening valve 23. The position, i.e., opening, of valve 23 is controlled by actuator 24, which is in turn responsive to a signal from a controller 82 whose set point is supplied by a Digital to Analog Convertor Element 71 in response to a signal from a computer control unit 31.

Computer control unit31 is preferably a general purpose digital computer that includes the usual inputoutput devices, memory, arithmetic unit and transfer buses. The computer is preferably programmed to perform a number of operations in sequence. The operations important to the calculation of the set point for temperature controller 82 are indicated in the Figure as boxes indicative of computer elements. Each of these operations is well known and can be performed by many existing general purpose computers. In the alternative, it is to be understood that a special purpose computer including each of the elements illustrated in computer control unit 31 can be employed.

Computer control unit 31 responds to signals indicative of the moisture contents of the cut rolled stems and laminae fed into dryer 17, as well as the moisture of tobacco on conveyor 20, after it has been conditioned by dryer l7 and cooler 19 and prior to the tobacco being fed to storage unit 21. The moisture contents of the cut rolled stems and laminae are determined by control unit 31 on the basis of moisture weight per unit time of the cut rolled stems and laminae fed to the dryer. To these ends,

weigher belts

13 and 14 are provided with transducers for deriving analog output signals W1 and W2 on

leads

32 and 33 which are indicative of the weights of tobacco on the

belt weigher units

13 and 14. Moisture of the cut rolled stems, laminae and material on conveyor 20 is determined as a percentage of total weight by

transducers

34, 35 and 36, respectively. Transducers 34-36 can be of any well known type, such as an infrared photoelectric transducer or a dielectric transducer. The analog signals derived by the belt weighers on

leads

32 and 33, as well as by moisture transducers 34-36, are converted into digital signals by analog-to-digital converters 37-41, one of which is responsive to each of the analog signals. In the alternative, a single analog-to-digital transducer can be provided and its inputs and outputs multiplexed between the several analog sources and the memory included in computer control unit 31. The converters respond for a predetermined time interval to average their input signals over the interval so that the signals can be considered as representative of the monitored quantity for each sample interval. The output signals of the converters are periodically sampled and supplied to the remainder of unit 31.

The digital signals are processed in computer control unit 31 so that the computer is responsive, at any one time, to signals corresponding with the identical mass of material by suitably delaying the signals from the several transducers and by delaying signals generated internally of the computer. The synchronized signals are combined so that the weights of water actually removed from the laminae and from the cut rolled stems are respectively calculated in accordance with:

LWR=(Ml) (W1) (OMR) [(Wl) (l Ml)] CWR =(M2) (W2) -(OMR) [(W2) (1 -M2)] where:

W1 and W2 are given supra,

M1 and M2 are the moisture values derived by analog-to-

digital converters

40 and 38 for the moisture measurements derived by

gauges

35 and 34 during one sampling period of the converters,

OMR M3/l M3 a set point for desired fraction of the moisture weight (M3) in the total weight of the dried tobacco on conveyor 20. The calculated values indicative of the weight of water removed from the laminae and cut rolled stems, as determined by Equations l) and (2), are combined in accordance with:

JDY= LWR (Al) (CWR) where:

A1 =a predetermined constant related to the relative ability of dryer 17 to remove moisture from the cut rolled stems compared to the laminae. The value of JDY in Equation (3) is a primary variable to determine the feed forward component of the expression that determines the temperature set point for controller element 82.

To calculate the value of JDY, the digital output signals of converters 37-40 are processed initially to calculate the moisture weight of the cut rolled stems and laminae during each sampling cycle of the analog-todigital converters. Considering the channel for determining the moisture weight of the cut rolled stems, the output signal of converter 37 is synchronized with that of converter 38 by delay element 42. The output signal of converter 38, a digital signal always having a value of less than one and indicative of the fraction (by weight) of the moisture in the tobacco monitored by gauge 34, is reversed in polarity and subtracted from one in element 42, which derives a (l M2) output signal indicative of the bone dry (i.e., weight of solid material with no moisture) weight of the cut rolled stems. The (l M2) output signal of element 42 is multiplied by the delayed output of element 42 in element 53, which derives an output signal (W2) (1 M2), indicative of the bone dry cut rolled stems weight during each sample cycle of

converters

37 and 38. A similar computation is performed by

elements

45, 46 and 54 to derive digital signals indicative of the bone dry weight of the laminae during each sample cycle of

converters

39 and 40.

The output signals of

elements

54 and 53 are combined with a signal indicative of the set point, OMR, for the moisture percentage per unit weight of tobacco moving on conveyor 20. The OMR set point is supplied to

multiplication elements

47 and 44 which are also responsive to the delayed outputs of

elements

54 and 53, whereby the multiplier elements respectively derive signals represented by (OMR) (W1) (l M1) and (OMR) (W2) (1 M2). The signals derived by

multiplier elements

47 and 44 respectively represent the expected moisture weight per unit time in the cut rolled stems and laminae of the conditioned tobacco on conveyor 20. Deviations from the expected performance are corrected by a feed back loop described infra.

To determine the amount of moisture, in terms of weight, to be removed by the dryer 17 from the cut rolled stems and the laminae, the signals derived by

elements

44 and 47 are compared with the weight of the moisture of the cut rolled stems and laminae initially fed into the dryer. To derive indications of the weight of the cut rolled stems and laminae fed into dryer 17, the outputs of

delay elements

42 and 45 are respectively combined with the outputs of

converters

38 and 40 in multiplying

elements

56 and 55 which derive output signals represented by M l W] and M2 W2. The MlWl and M2W2 signals derived by

multiplier elements

56 and 55 are compared with the computed quantities indicative of the moisture weight of the cut rolled stems and laminae as derived from multiplying

elements

44 and 47; the comparison operations are respectively performed by

subtraction elements

57 and 56 which derive digital output signals represented by Equations (1) and (2) supra. The output signals of

subtraction elements

57 and 56 are respectively delayed in

delay elements

49 and 48 in accordance with the dynamic characteristics of the dryer.

To provide for the differential effect of dryer 17 on a pound of moisture in the cut rolled stems relative to a pound of moisture in the laminae, the output signal of one of

elements

48 and 49 is modified by a predetermined factor indicative of the difference in the ability of the dryer to dry the two different sources of tobacco fed thereto. In the present embodiment, the output signal of delay element 48 is multiplied by a predetermined constant, having a value less than one since it is assumed that the dryer is more effective in removing a pound of moisture from the cut rolled stems than from the laminae; the multiplication operation is performed by multiplying the output of delay element 48 with the predetermined constant Al in multiplier element 58. The output signal of multiplier element 58, indicative of the drying rate of dryer 17 for the cut rolled stems, is combined in adder element 59 with the output signal of delay element 49, indicative of the rate at which dryer 17 should remove moisture from the laminae. The output signal of adder element 59, as expressed by Equation (3) supra, is averaged in averaging element 61 over a number of cycles of converters 37-40 to remove relatively high frequency transients by a process which is somewhat similar to a low pass filter operation.

The time averaged output signal of element 61, .151 is modified by a predetermined coefficient, B1, in multiplier element 62 which derives a digital signal that is combined with a predetermined constant, B0, indicative of the desired moisture of the conditioned tobacco on conveyor the combining operation is performed by adderelement63, which derives an output signal in QCCOI'GQIE? with the linear, polynomial expression B0 B1 (JDY). While the signal derive ti l )y element 63 is a linear polynomial of the quantity JDY, the output signal could be a higher order polynomial, or any other suitable function. The signal derived by element 63 is indicative of a component of the set point temperature required to achieve the desired moisture of the conditioned tobacco on conveyor 20. The signal is derived basically by feed forward techniques in response to measurements of the moisture of the cut rolled stems and the laminae, with consideration being taken for the differential effect of dryer 17 on a pound of moisture in the cut rolled stems relative to a pound of moisture in the laminae.

The feed forward component reflecting the drying rate of dryer 17 due to the moisture weight of the cut rolled stems and laminae is combined with a feed back component derived by a proportional-integral feed back loop. To derive the feed back component, the output of digital-to-analog converter 41, responsive to moisture gauge 36 which monitors the conditioned tobacco on conveyor 20, is fed to a proportional-integral "element 64, of a well known type, which is also responsive to a digital moisture set point signal. Proportionalintegral element 64 derives an error signal indicative of the difference between the moisture set point signal and the output of converter 41 during each sample cycle of the converter, integrates the error signal and adds the integrated error signal to the error signal to derive the second component for the set point temperature of dryer 17.

The output signals of proportional-integral element 64 and the feed forward signal derived by adder element 63 are combined in adder element 65, the output of which is indicative of the set point value for the temperature of dryer 17. The output set point signal from element 65 is supplied to controller 82 via digital to analog converter element 71.

A system basically similar to that illustrated in FIG. 1 for a rotary drum dryer 17 can also be employed in conjunction with a fluidized dryer, such as illustrated in FIG. 2. In the system of FIG. 2, moist cut rolled stems and laminae are fed from suitable sources, past weight and moisture transducers to conveyor 101 in the same manner that the weight and moisture of cut rolled stems and laminae are monitored and fed to conveyor 18 in the system of FIG. 1. The transducers derive signals indicative of the weight and moisture of the cut rolled stems and laminae and feed these signals into computer 102 which functions in a manner similar to the computer 31 of FIG. 1 to derive a control signal for actuator 103 of stem valve 104.

The tobacco on conveyor 101 is fed via rotating star valve 105 close to the bottom ofupdraft leg 107 of vertically oriented drying chamber 106. The tobacco is fluidized in drying chamber 106 by hot air introduced into the bottom of the drying chamber, whereby the fluidized tobacco rises in leg 107 of the drying chamber, and thereafter descends in leg 108. A number of drying chambers similar to chamber 106 can be provided, or a single drying chamber can be included as illustrated. Fluidized, dry tobacco descending in leg 108 is fed into separator 109, which functions to separate the relatively light, hot air from the conditioned tobacco. The conditioned tobacco emerges from separator 109 through the bottom thereof and is fed via star valve 111 to output conveyor 112. The moisture of tobacco on output conveyor 112 is monitored by moistu're transducer 113 which supplies an input signal to computer 102.

Air emerging from separator 109 in conduit 114 frequently includes a significant amount of dust which is separated. To this end, conduit 114 is connected to cyclone separator 115 via pump 116. Cyclone separator 115 separates the dust from the air, whereby the dust falls by gravity downwardly in the separator and the dust-free air emerges from the top of separator into conduit 117. A portion of the air in conduit 117 is exhausted to the'atmosphere via conduit 118, while the remaining, major portion of the air in conduit 117 is fed back to the bottom of drying chamber 106 via heater 121. Heater 121 is also responsive to fresh, inlet air coupled through conduit 122 in controlled amounts.

Heater 121 is preferably a steam heater that does not add'moisture to the air passing through it. Steam is fed in controlled amounts through valve 104 into dryer 121 to control the temperature of the air current that are fluidizes the tobacco in chamber 106. The position of valve 104, and thereby the heat exchange propertiesof the heat exchange fluid supplied to the dryer that affects the dryer drying rate, is determined by set point signals derived by the moisture and weight transducers which feed signals to computer 102 to determine a set point for the temperature inside of drying chamber 106. The temperature set point is calculated in a manner similar to that described with regard to FIG. 1, taking into consideration the differential drying effects of chamber 106 on the cut rolled stems and laminae. The temperature set point is compared with the actual temperature within drying chamber 106, as monitored by temperature probe 123 that is positioned in a region of the drying chamber through which tobacco flows. The signal derived by temperature probe 123 is fed to computer 102 so that it can be compared with the derived set point signal to control actuator 103 and the position of valve 104.

While there have been described and illustrated several specific embodiments of the invention, it will be clear that variations in the details of the embodiments specifically illustrated and described may be made without departing from the true spirit and scope of the invention as defined in the appended claims.

We claim:

1. In a system for controlling the amount of moisture removed by a dryer from a stream of tobacco formed by mixing a supply of cut rolled stems with a supply of laminae comprising means for deriving first and second signals respectively indicative of the amounts of moisture in the cut rolled stems fed to the dryer and the laminae fed to the dryer, means for modifying one of said signals relative to the other signal in accordance with the relative ability of the dryer to remove moisture from the cut rolled stems and the laminae to derive signals respectively indicative of controls for the drying rates of the dryer for the cut rolled stems and laminae, and means responsive to the signals indicative of dryer drying rates for deriving a feed forward control signal for heat exchange properties of a fluid supplied to the dryer and affecting the drying rate of the dryer.

2. The system of claim 1 wherein the means for deriving a control signal includes means for linearly combining the signals indicative of the dryer drying rates.

3. In a system for controlling the amount of moisture removed by a dryer from a stream of tobacco formed by mixing a supply of cut rolled stems with a supply of laminae comprising means for deriving first and second signals respectively indicative of the amounts of moisture in the cut rolled stems fed to the dryer and the lam inae fed to the dryer, means for modifying one of said signals relative to the other signal in accordance with the relative ability of the dryer to remove moisture from the cut rolled stems and the laminae to derive signals respectively indicative of controls for the drying rates of the dryer for the cut rolled stems and laminae, and means responsive to the signals indicative of dryer drying rates for deriving a control signal for the drying rate of the dryer, said means for deriving a control signal including means for linearly combining the signals indicative of dryer drying rates to derive another signal, and means for time averaging the another signal.

4. The system of claim 3 further including means for multiplying said time averaged another signal by a first predetermined constant, and means for linearly combining a further signal indicative of a second predetermined constant with said multiplied time averaged another signal, said first and second constants being determined by properties of the dryer.

5. A method of controlling the amount of moisture removed by a dryer from a stream of tobacco formed by mixing a supply of cut rolled stems with a supply of laminae comprising the steps of measuring the amounts of moixture of the cut rolled stems fed to the dryer and the laminae fed to the dryer to derive first and second signals respectively indicative of moisture weight of the cut rolled stems and laminae fed to the dryer, modifying one of said signals relative to the other signal in accordance with the relative ability of the dryer to remove moisture from the cut rolled stems and the laminae to derive feed forward signals respectively indicative of controls for the drying rates of the dryer for the cut rolled stems and laminae, and controlling heat exchange properties of a fluid supplied to the dryer and affecting the dryer drying rate in response to the signals indicative of the dryer drying rates for the cut rolled stems and laminae.

6. A system for controlling the amount of moisture removed by a dryer from a stream of tobacco formed by mixing a supply of cut rolled stems with a supply of laminae comprising gauge means for deriving first and second signals respectively indicative of the moisture weights of the cut rolled stems fed to the dryer and the laminae fed to the dryer, means for modifying one of said signals relative to the other signal in accordance with the relative ability of the dryer to remove moisture from the cut rolled stems and the laminae to derive feed forward signals respectively indicative of controls for the drying rate of the dryer for the cut rolled stems and laminae, and means responsive to the signals indicative of the dryer drying rates for controlling heat exchange properties of a fluid supplied to the dryer and affecting the drying rate of the dryer.

7. A computer controlled method of controlling the amount of moisture removed by a dryer from a stream of tobacco formed by mixing a supply of cut rolled stems with a supply of laminae comprising the steps of measuring the amounts of moisture of the cut rolled stems fed to the dryer and the laminae fed to the dryer to derive first and second signals respectively indicative of moisture weight of the cut rolled stems and laminae fed to the dryer, responding to the indications to derive first and second signals respectively indicative of the amounts of moisture in the cut rolled stems fed to the dryer and the laminae fed to the dryer, modifying one of said signals relative to the other signal in accordance with the relative ability of the dryer to remove moisture from the cut rolled stems and the laminae to derive signals respectively indicative of controls for the drying rate of the dryer for the cut rolled stems and laminae, and deriving a feed forward control signal for the drying rate of the dryer in response to the signals indicative of the dryer drying rates for the cut rolled stems and laminae, and in response to the control signal controlling heat exchange properties of a fluid supplied to the dryer and affecting the dryer drying rate.

8. In a system for controlling the amount of moisture removed by a dryer from a stream of tobacco formed by mixing a supply of cut rolled stems with a supply of laminae comprising means for deriving first and second signals respectively indicative of the amounts of moisture in the cut rolled stems fed to the dryer and the laminae fed to the dryer, means for modifying one of said signals relative to the other signal in accordance with the relative ability of the dryer to remove moisture from the cut rolled stems and the laminae to derive feed forward control signals respectively indicative of feed forward controls for the drying rate of the dryer for the cut rolled stems and laminae, means for deriving a feed back control signal in response to the moisture of the tobacco dried by the dryer, and means responsive to the feed forward control signals and the feed back control signal for deriving a control signal for the drying rate of the dryer.

9. The system of claim 8 wherein the means for deriving a feed back control signal includes a proportionalintegral controller responsive to a set point for the moisture of tobacco dried by the dryer and the indication of the moisture of the tobacco dried by the dryer.

10. The system of claim 9 wherein the means for deriving a control signal includes means for deriving a set point for the dryer temperature, means for deriving a signal indicative of the dryer temperature, and means for comparing the dryer temperature set point and the signal indicative of the dryer temperature to derive a signal for controlling the dryer temperature.

11. In a system for controlling the amount of moisture removed by a dryer from a stream of tobacco formed by mixing a supply of cut rolled stems with a supply of laminae comprising means for deriving first and second signals respectively indicative of the amounts of moisture of the cut rolled stems fed to the dyer and the laminae fed to the dryer, means for deriving a third signal indicative of the moisture of thetobacco dried by the dryer, means combining said first and third signals for calculating the amount of moisture removed by the dryer from the cut rolled stems and combining said second and third signals for calculating the amount of moisture removed by the dryer from the laminae, and means for modifying one of said calculated moisture amounts relative to the other calculated moisture amount to derive feed forward signals respectively indicative of controls for heat exchange properties of a fluid supplied to the dryer and affecting the dryer drying rate due to the cut rolled stems and the laminae.

12. In a system for controlling the amount of moisture removed by a dryer from a stream of tobacco formed by mixing a supply of cut rolled stems with a supply of laminae comprising means for deriving signals respectively indicative of the amounts of moisture to be removed by the dryer from the cut rolled stems and the laminae, and means for modifying the value of one of said derived moisture amount indicating signals relative to the other derived moisture amount indicating signal to derive feed forward control signals respectively indicative of controls for heat exchange properties of a fluid supplied to the dryer and affecting the dryer drying rate due to the cut rolled stems and the laminae.

13. In a system for controlling the amount of moisture removed by a dryer from a stream of tobacco supplied to the dryer comprising measuring means responsive to the weight of tobacco in the stream for deriving a first signal commensurate with the tobacco weight, measuring means responsive to the moisture percentage by weight of tobacco in the stream for deriving a second signal commensurate with the tobacco moisture percentage by weight, computing means, including multiplying means responsive to the first and second signals, for deriving a feed forward signal having a value commensurate with the amount of moisture, by weight, to be removed from the tobacco by the dryer, and means responsive to the feed forward signal to derive a control signal for controlling heat exchange properties of a fluid supplied to the dryer and affecting the dryer drying rate.

14. The system of claim 13 wherein the computing means is responsive to a third signal indicative of the moisture of the tobacco dried by the dryer.

15. The system of claim 14 wherein the first, second and third signals have magnitudes respectively represented by W, M, and OMR, and said computing means includes means for deriving a signal having a magnitude represented by feed forward signal to derive the control signal.

Claims

3. In a system for controlling the amount of moisture removed by a dryer from a stream of tobacco formed by mixing a supply of cut rolled stems with a supply of laminae comprising means for deriving first and second signals respectively indicatiVe of the amounts of moisture in the cut rolled stems fed to the dryer and the laminae fed to the dryer, means for modifying one of said signals relative to the other signal in accordance with the relative ability of the dryer to remove moisture from the cut rolled stems and the laminae to derive signals respectively indicative of controls for the drying rates of the dryer for the cut rolled stems and laminae, and means responsive to the signals indicative of dryer drying rates for deriving a control signal for the drying rate of the dryer, said means for deriving a control signal including means for linearly combining the signals indicative of dryer drying rates to derive another signal, and means for time averaging the another signal.

9. The system of claim 8 wherein the means for deriving a feed back control signal includes a proportional-integral controller responsive to a set point for the moisture of tobacco dried by the dryer and the indication of the moisture of the tobacco dried by the dryer.

11. In a system for controlling the amount of moisture removed by a dryer from a stream of tobacco formed by mixing a supply of cut rolled stems with a supply of laminae comprising means for deriving first and second signals respectively indicative of the amounts of moisture of the cut rolled stems fed to the dyer and the laminae fed to the dryer, means for deriving a third signal indicative of the moisture of the tobacco dried by the dryer, means combining said first and third signals for calculating the amount of moisture removed by the dryer from the cut rolled stems and combining said second and third signals for calculating the amount of moisture removed by the dryer from the laminae, and means for modifying one of said calculated moisture amounts relative to the other calculated moisture amount to derive feed forward signals respectively indicative of controls for heat exchange properties of a fluid supplied to the dryer and affecting the dryer drying rate due to the cut rolled stems and the laminae.

15. The system of claim 14 wherein the first, second and third signals have magnitudes respectively represented by W, M, and OMR, and said computing means includes means for deriving a signal having a magnitude represented by (M) (W) - (OMR) (W) (1 -M).

16. A system of claim 15 wherein OMR is a predetermined magnitude commensurate with M3/1 - M3, where M3 is a set point value for desired fraction of moisture weight in the total weight of dried tobacco obtained from the dryer.

17. A system of claim 14 further including means for measuring the moisture of tobacco after the tobacco has passed through the dryer and for deriving a feedback signal commensurate with the measured moisture of the tobacco after it has passed through the dryer, and means for combining the feedback signal with the feed forward signal to derive the control signal.