US2981986A

US2981986A - Control apparatus and methods

Info

Publication number: US2981986A
Application number: US555560A
Authority: US
Inventors: Hugh G Neil
Original assignee: SPECIAL INSTR LAB Inc
Current assignee: SPECIAL INSTR LAB Inc; SPECIAL INSTRUMENTS LABORATORY Inc
Priority date: 1955-12-27
Filing date: 1955-12-27
Publication date: 1961-05-02
Anticipated expiration: 1978-05-02

Description

May 2, 1961 H. G. NEIL CONTROL APPARATUS AND METHODS 2 Sheets-Sheet 1 Filed Dec. 27, 1955 IN VENTOR ATTORNEYS y 1961 H. G. NEIL 2,981,986

CONTROL APPARATUS AND METHODS Filed Dec. 27, 1955 2 Sheets-Sheet 2 as ski/4:74;,

IN VENTOR ATTORNEYS U t d St t s 2,981,986 ooNTRoL APPARATUS AND arnons Hugh G. Neil, Knoxville, Tenn., assignor to Special In: Incorporated, Knoxville, Tenn.,

struments Laboratory, a corporation of Tennessee rue nec. 27, 1955, Ser. No. 555,550 4Claims. CI. 19-70) uniformity in the products. This difficulty is due in part i to the impossibility of assembling an elongated body of fibers in such a way that the body will have complete uniformity, and in part to irregularities which are introduced by the machinery which handles the body of fibers.

According to the present day commercial practices, attempts are made to control yarn uniformity at two points in the yarn making process. The first of these points is at the picker, the machine which serves to place the fibers in the form of a lap or mat. Although uniformity control at this stage of the process may be desirable in some respects, it is difficult to achieve because of the nature of the picking operation. Moreover, control at this stage does not assure yarn uniformity because of the many conditions, to variations in the mass of an elongated asvariations which are introduced by the machinery which I follows the picker. The card, for example, completely transforms the lap from the picker. 7 The other point in the process at which uniformity control has been attempted is the drawing frame. This apparatus serves to attenuate the slivers produced by the card. The control exercised in present day commercial practice consists of periodically taking samples of the slivers delivered fromthe drawing frame, weighing these samples, and then adjusting the draft ratio of the machine. It will be evident that this method lacks the continuity necessary for assuring the production of truly uniform yarns.

A number of proposals have been advanced directed to continuous control of the drawing frame. These pro-l posals contemplate sensing the mass of the sliver travelling through the frame and thenautornatically adjusting the draft ratio of the frame in,,r,esponse to the values sensed. Such proposals have notcome into 'general commercial use fo r'anumber ofreason s."

One important shortcoming in the systems heretofore proposed was that the sensing, apparatus employed did not respond accurately, under mill conditions, to variations in the mass of the slivers. Photoelectric detectors respond to the shape, or shadow, characteristics of a sliver, rather than to its mass. Dielectric detectors also are affected bythe shape of the sliver, and additionally,

they are very sensitive to the humidity conditions prevailing in the mills. Similar problems have been. associated'with the various other types of detectors which have been used heretofore. t v I Another important shortcoming in the prior art systerns isth at they respond to shortterm variations in the slivers,' but are unstable to'long term variations. "With this type of control the benefits realized .areyerylimited even wheii'the'equipment is working properly. If the draft fatio is to be changed quickly enough to remove a t ea bis i. mai s. randma ae 9 t a the sliveiyt'he*responsetimes' for alrof the sensing and controlling devices must be very short, and oscillation, or hunting, of the system frequently occurs, often introduce j ing additional nonuniformity. Moreover, a system which is designed to respond to short term variations usually cannot cope effectively with long term variations in the slivers.

The inability of the prior art systems to effectively reations.

An object of the present invention is to provide apparatus and methods for automatically controlling the d ce. J gree of attenuation of a body of fibers in response to the mass of the body. In particular, it is an object of the invention to provide apparatus and methods for automatically adjusting the draft ratio of a drawing frame in response to variations in the mass of the sliver being drafted by the drawing frame.

Another object of this invention is to provide sensingapparatus which responds accurately, under textile mill' sembly of fibers.

Another object of this invention is to provide apparatus and methods for sensing long term, i.e., yard-toyard, variations in'the' mass of an axially advancing as sembly of fibers, and for controlling the attenuation of such assembly inresponse to the values sensed. In this. manner, the need for extensive, doubling is eliminated, and fewerfiber handling steps are required in the pro duction of. yarn. Thus, the cost is reduced, and the short term uniformity is automatically improved.

Still another object of this invention is theprovision of apparatus and methods for controlling notonly the long term, but also the short term variations in asliver.

The foregoing and other objects of this invention may be realized by the association with a drawing frame of a beta ray detector or sensing apparatus for continuously measuring the mass of the sliver being drafted on the frame andcontrol means operating in response to the beta ray detector for changing the draft ratio of the frame. The beta ray detector should have a long time constant so that it is relatively insensitive to shortterm variations in the sliver. Where both long term and short term variations are to be controlled, two detectors should be employed, one having a longtime constant and the other having a short time constant, andthe control means should operate in response .to both detectors.

A better understanding of this invention and of its many advantages will be gained from the following detailed: description of certain embodiments thereof illustrated in the accompanying drawings, in which:

Fig. 1 is ,a diagrammatic perspective view illustrating a drawing frame controlled in accordance with thepresent invention;

Fig. 2 is a cross sectional view of a beta ray absorber which may be used in the combination of Fig. 1;

Fig. 3 is a circuit diagram showing a circuit suitable for use in the apparatus of Fig. l; and

Fig. 4 is a diagram illustrating another embodiment of the invention.

In Fig. l, the sliver 2 is fed successively between the rolls of a pair of feed rolls 4, and a pair of delivery rolls 6. These rolls are supported in the usual way in a machine framestructure 7, the illustration of which is largely diagrammatic. The lower roll of each pair is driven by means which will be described belomand the 1121 61111011 of each pair is urged toward the lower roll by weight Pa ented ,Msn 1 6.1.

slivers are combined in the drafting frame to produce a single sliver of a weight which may be comparable to the weight of each of the individual slivers fed to the frame; This procedure is often referred to as doubling, and it is well understood in the art. One of its objects is to eliminate long term variations in the weight of the slivers.

Although only two pairs of rolls have been illustrated in Fig. 1, it will be understood by persons skilled in the art that the drawing frame may include several pairs of rolls and that the omission of certain of the rolls from Fig. 1 represents merely an attempt to simplify this disclosure. The present invention is applicable to all types of drafting apparatus.

As the sliver 2 is fed from the delivery rolls 6, its mass is sensed by a detector or sensing apparatus indicated generally by the numeral in Fig. 1. This detector preferably is a beta ray detector. It includes a housing 12 for a source of radioactive material, a housing 14 for an ionization chamber on the opposite side of the sliver 2 from the source of radio active material, a housing 16 for another ionization chamber disposed on the same side of the sliver 2 as the source of radioactive material, and a housing 18 for an absorber located between the source of radio active material and the ionization chamber in the housing 16. The details of the constructions of the housings 12, 14, and 16, form no part of the present invention, and they will not be described in detail. The functions of the various elements of the detector 10 will be evident from a consideration of Fig. 3, to be described later.

Fig. 2 represents a vertical cross section through the housing 18 for an absorber indicated by the numeral 20. This absorber 20 may take a variety of forms. As illustrated, it is a wedge-shaped mass of paper, plastic, or other material. This absorber 20 is mounted in the housing 18 for horizontal movement with respect to the openings 21 in the housing 18 to position portions of difierent thicknesses in the path of the beta rays passing through said openings 21. In this way, the rate of absorption of rays by the absorber may be regulated.

Horizontal movement of the absorber 20 is brought about by rotating a hand wheel 22 fixed to a shaft 24, threadedly mounted in the housing 18 and extending inwardly into engagement with a socket 26 attached to the absorber 20. The absorber is held against rotation with the shaft 24 by laterally projecting lugs, not illustrated, which ride in a groove 27 in the casing wall.

Referring now to Fig. 3 of the drawings, the source of beta rays is indicated by the numeral 28. This is preferably radio strontium, but it will be evident that other sources, such as radio thallium, may be used if desired. The energy level of the beta rays emitted by radio strontium make it a particularly desirable source for use in a detector associated with a drawing frame because this energy level is such that, in a properly constructed apparatus, approximately one-half of the beta rays entering a 50 grain sliver spaced approximately one inch from a radio strontium source are absorbed by the sliver. With this rate of absorption, the apparatus is particularly sensitive to the sliver variations to be detected.

The ionization chambers disposed in the housings 14 and 16 are designated in Fig. 3 by the

numerals

30 and 32, respectively. One terminal of each such chamber is connected to a source of positive potential, designated B while the other terminal is connected to ground through a resistance. The resistances for the

chambers

30 and 32 are designated in Fig. 3 by the numerals 34 and 36,

Moreover, since the only rays which may enter an ionization chambers are those which are not absorbed by materials disposed intermediate the radiation source and the chamber, the rate of entrance of rays into a chamber varies inversely with the rate of absorption of rays by intermediate materials. 7

As explained above, the rate of absorption of beta rays by the sliver 2 is very closely related to the mass of the sliver. Thus, the degree of ionization of the gas in chamber 30 is a function of the mass of the sliver. Similarly, the rate of absorption of rays by the absorber 20 depends upon the mass of the portion of the absorber disposed in the path of the rays, and the degree of ionization of the gas in chamber 32 is a measure of such mass.

It has been found that the beta ray type of sensing apparatus gives exceptionally fine results under textile mill conditions. This type of apparatus is not very sensitive to either the shape of the sliver or to the humidity conditions in the mill. In these respects it is far superior to the detectors heretofore proposed for use in systems for controlling drafting operations.

Another advantage of the beta ray detector over the detectors of the prior art is that a certain amount of control over the static electricity in the slivers is achieved by the ionized air in the path of the beta rays. This control effect contrasts sharply with the results brought about by a dielectric detector in the presence of static charges on the fibers.

Initially, the position of the absorber 20 is adjusted so that it will absorb beta rays at the same rate as a sliver of the desired mass. As long as the mass of the sliver corresponds to the desired mass, the degrees of ionization attained in the two

chambers

30 and 32 will be approximately equal. When, however, the mass of the sliver 2 departs from the desired value, there will be a difference in the degrees of ionization in the two

chambers

30 and 32.

It should be noted that the use of two ionization chambers automatically compensates for changes in the emission characteristics in the source of radio active material. Radio strontium and radio thallium have relatively short half lives, and it is desirable that means be provided for making the necessary compensation automatically. However, it will be understood that such compensation may be accomplished by means other than that shown, such as, for example, by a suitable electric balancing circuit.

The difference in the degrees of ionization in

chambers

30 and 32 is measured by a pair of electrometer tubes 38 and 40. The outputs from the electrometer tubes 38 and 40 are fed to a push-pull D.C. amplifier 42 and then to a phase converter 44 for converting the DC. signals to A.C. signals. The A.C. signals from the phase converter 44 are amplified by an A.C. amplifier 46 and by a power amplifier 48. The plate circuit of the power amplifier 48 includes a coil 50 of a two-phase servo motor 52, the field coil of which is indicated by thenumeral 54.

Other possible circuits for the

ionization chambers

30 and 32 will be obvious to persons skilled in the art. For example, the collecting potential in one chamber could be held positive while the collecting potential in the other chamber was held negative, and the collecting electrodes could be connected together and caused to operate a single electrometer tube. -An obvious advantage of such a circuit is that it would be independent of high valued resistors, such as the resistors 34 and 36 of Fig. 3.

It should be noted that the A.C. supply for the phase converter 44 includes a transformer 56 and a capacitance 58. With this arrangement, the phase of the signal from the phase converter 44 is shifted approximately degrees with respect to the current in the field coil 54. In operation, the circuit of Fig. 3 causes the two-phase servo motor 52 to rotate in one direction when the mass of the sliver 2 is below the desired value, and in the opposite direction when the mass of the sliver is above the desired value.

The circuit just described operates in a predetermined I,

time relationship with respect to the speed of the sliver passing through the path of'the betarays. This-relationship, enables the apparatus to respond to long term, i.e., yard-to-yard, variations in the mass of the sliver. In particular, it iscontemplated that the response characteristics of the sensing circuits shall be such that, if an instantaneous change in the mass of the sliver occurs, the

circuits will respond so as to reflect a change approximatingtwo-thirds of the instantaneous change in the mass of the sliver in the cours'eof a time interval which is at least; as long as the time interval required for the passage of one yard of the sliver through the path of the beta rays. I

The response characteristics of the electric circuit illustrated in Fig. 3 can be described approximately in terms of a first order ditferential'equation which includes a time constant for the circuit. For the usual drawing frame, in which thedelivery speed of the sliver may be from approximately one hundred to three hundred yards per minute, the timeconstant of a sensing circuit should be between one-tenth of a second and ten seconds.

Referring'againto Fig. 1, it will be seen that the mechanical output from the two-phase servo motor 52 is transmitted through a shaft 60 to an infinitely variable transmission 62. The details of the transmission 62 have not been illustrated in the drawings because these form no part of the present invention. A suitable transmission would be the Graham Variable Speed Transmission Model 1250M;

Since the control system of this invention includes three elements, that is, the sensing circuit, the servo motor 52, and the variable transmission 6-2, it is necessary to consider the relationships between the response times of these elements. If oscillation of the overall system is to be avoided, it is necessary that one of the elements of the system have a response period which is significantly longer than the response periods for the other elements. According to the present invention, therefore, the time constants of the various elements are so related that the sensing circuit responds much more slowly than either the servo motor 52 or the variable transmission 62. In particular, it is intended that the response of. both the servo motor and the variable transmission 62 should be at least four times as fast as that of the sensing circuit.

The drive systems for the pairs of rolls 4 and 6 now will be apparent. The shaft of the bottom delivery roll 6 is driven at a constant speed by a belt 64 passing around a pulley 66 fixed to the roll shaft and a pulley 68 fixed to the shaft of an electric motor 70. The bottom feed roll 4 is drivingly' connected to the shaft of the bottom delivery roll 6 through the variable transmission 62, a drive belt 72, and a pair of pulleys 74 and '76. Hence, by adjusting the transmission 62, it is possible to change the draft ratio,.i.e., the ratio of the circumferential velocity of the delivery rolls 6 to the circumferential velocity of the feed rolls 4.

In operation", the control system serves to adjust the draft ratio so as to counteract or eliminate the mass variations detected by the sensing circuits. When the sliver passingthe detector is heavier than the desired value, the servo motor 52 rotates in one direction and adjusts the variable transmission 62 so as to slow down the feed rolls 4 to thereby increase the draft ratio of the frame. Increased attenuation of the sliver then returns the sliver to the desired weight. Underweight portions of slivers are taken care of in a similar manner.

When the present invention is employed in the yarn making process, it is pssible to obtain yarns of good uniformity with a reduction in the number of drafting operations which take place. In this connection, it is pointed out that reducing the number of drafting operations is desirable not only because it reduces the amount of equipment needed, but also because it reduces the nep count of the yarns produced. It is well known that the more a group of fibers is handled, the greater the number assnaeaa ofneps in it,become., It,is alsopossibletoeliminate uni-u:

formity control of the picker,-if desired.

The embodiment of the invention illustrated in Fig. 4 of the drawings includes a pair of feed rolls and a pair of delivery ,rolls 82, .which may correspond, respectively, to the feed rolls 4 and the delivery rolls 6 in Fig. 1. A sliver 84 passes through a first or short term variation detector on its way between the feed rolls 80 and the delivery rolls 82, and through a second or long term variation detector rolls 82.

The long term variation detector may correspond in all respects to the detector 10 of Fig. 1. Its function is to ascertain the long term variations in the mass of thesliver being drafted, and for this purpose it should be located outside of the drafting zone, as shown.

The short term'variation detector, on the other hand, is utilized to measure the short term variations in the sliver, and for this purpose, it should be located close to the point of control, that is, close to the drafting zone. The short term variation detector maybe a beta ray de tector, or it'maybe some other type, if desired. Its time constant should be such that it is sensitive to inch-by-inch variationsin the sliver. As an example, the time constant might correspond to the time interval required for one to several inches of sliver to pass the detector.

Several types of detectors are suggested in the patent to Hare, No. 2,682,l44, granted June 29, 1954. It is possible to construct some of these detectors with very short time constants, and the use of such detectors may be desirable in some instances. However, the beta ray detector normally is preferable because of its accuracy in sensing mass.

According to Fig. 4, both long term and short term variations in the density of the sliver 84 are compensated for. The output from the long term variation detector operates a servo mechanism which adjusts the short term variation detector so as to vary the standard with which the mass of the sliver is to be compared by the short term variation detector. As an example, the servo mechanism can take the form of a two-phase motor, such as the motor 52 of Fig. l, and the output from this motor can be geared to a shaft, such as the shaft 24 shown in Fig. 2, for adjusting the position of an absorber.

The output from the short term variation detector operates a servo mechanism which serves to adjust a control mechanism for varying the draft ratio between the feed rolls 80 and the delivery rolls 82. The servo mechanism and the control mechanism may correspond in all respects to the servo motor 52 and the variable transmission 62 of Fig. l.

Although certain embodiments of this invention have been described in detail, various alterations and modifications will be apparent to persons skilled in the vart. Moreover, it will be obvious that certain features of the invention have utility in combinations other than those described specifically above. Consequently, it is intended that the foregoing description should be considered as exemplary only, and that the scope of the invention be ascertained from the following claims.

I claim:

l. A method of controlling drafting apparatus so as I to minimize variations in the mass of a sliver or the like, which comprises sensing short term mass variations of the sliver as it passes through the drafting zone, sensing long term mass variations of the drafted sliver, and changing the degree of draft imparted to said sliver by the drafting apparatus in response to both the long term and the short term variations sensed.

2. Apparatus for sensing variations in the mass of a sliver or the like, comprising means for advancing said sliver, a source of beta rays disposed adjacent the path of said sliver, a first ionization chamber disposed on the opposite side of said path from said source to receive beta rays which pass through said sliver, absorber means disas it emerges from the delivery.

posed so as to receive beta rays directly from said source and being adjustable so that the number of beta rays absorbed thereby may be changed, a second ionization chamber disposed on the opposite side of said absorber means from said source to receive beta rays which pass through said absorber means, and circuit means connected to said chambers and responding to differences in the degrees of ionization existing in said chambers.

3. Apparatus for controlling variations in the mass of a sliver or the like, comprising means for advancing and drafting said sliver, a source of beta rays disposed adjacent the path of said sliver, a first ionization chamber disposed on the opposite side of said path from said source to receive beta rays which pass through said sliver, absorber means disposed so as to receive beta rays directly from said source and being adjustable so that the number of beta rays absorbed thereby may be changed, a second ionization chamber disposed on the opposite side of said absorber means from said source to receive beta rays which pass through said absorber means, a two-phase servo motor having a shaft, circuit means connected to said chambers and to said motor for causing said motor shaft to rotate in one direction when the degree of ionization in said first chamber exceeds that in said second chamber and for causing said motor shaft to rotate in the opposite direction when the degree of ionization in said second chamber exceeds that in said first chamber, and variable transmission means operatively connected to said motor shaft and to said drafting means for changing the draft ratio of said drafting means.

4. Apparatus for controlling the mass-per-unit-length of a sliver or the like, comprising means for advancing and drafting said sliver, first and second sensing means disposed adjacent the path of said advancing sliver for continuously sensing the mass of said sliver, said first sensing means being responsive to short term variations in the mass of the sliver, said second sensing means being responsive to long term variations in the mass of the sliver, and variable transmission means for varying the draft ratio of said drafting means in response to both the long term and the short term variations sensed by said sensing means.

References Cited in the file of this patent UNITED STATES PATENTS 2,249,820 Gulliksen July 22, 1941 2,264,725 Shoupp et a1. Dec. 2, 1941 2,407,100 Richardson Sept. 3, 1946 2,565,734 Lundahl Aug. 28, 1951 2,612,743 Strother Oct. 7, 1952 2,750,986 Russell et a1. June 19, 1956 2,805,449 Martin Sept. 10, 1957 FOREIGN PATENTS 731,438 France Sept. 2, 1932 882,819 Germany July 13, 1953