US 3141202 A
Description (OCR text may contain errors)
3,141,202 DIFYING A. LINNERT ETAL CHINEIS FOR' CONTINUOUSLY MO July 21. 1964,
REGULARITY CONTROL IN MA A PROPERTY OF A MATERIAL PROCESSED THEREBY 1961 3 Sheets-Sheet 1 Filed Aug. 8,
TFL: .P La schiva o .Trou E f c July 2l, 1964 A.L1NNERT ErAl. 3,141,202
REGULARITY CONTROL 1N MACHINES FOR coNTmuousLY MODIFYING A PROPERTY oF A MATERIAL PRocEssEn THEREBY FiledAug. a, 1961 I5 Sheets-Sheet 2 INVE NTOR 5:
l Filed Aug. 8, 1961 July-21, 1964 A, UNNERT ETAL 3,141,202
REGULARITY CONTROL IN MACHINES FOR CONTINUOUSLY MODIF'YILNG` A PROPERTY oF A MATERIAL PROCESSED THEREBY 5 Sheets-Sheet 3 INVENTOR S:
United States Patent O 3,141,202 REGULARITY CONTRL IN MACHINES FOR CONTINU OUSLY MODIFYIN G A PROPERTY F A MATERIAL PROCESSED THEREBY Arthur Linnert and Harold Catling, Manchester, and Albert E. De Barr, Cheadle, England, assignors to The Cotton Silk and Man Made Fibres Research Association, a British association of Great Britain, Northern Ireland, and the Isle of Man Filed Aug. 8, 1961, Ser. No. 130,037 Claims priority, application Great Britain Aug. 13, 1960 7 Claims. (Cl. 19-240) This invention concerns machines for modifying a property (such as the density or cross-sectional dimensions) of a continuous length of material being processed thereby. Examples of such machines are scutchers, carding engines, lap forming machines and draw frames, all used in processing fibrous textile materials.
Attention has been directed in the past to the provision of control means for such machines which will enable a product of high regularity to be obtained. In scutchers for example, a control device designed many years ago has almost always been fitted to the feed mechanism of the machine. This control device operates on an open loop system, the varying deflection of pedals disposed beneath the feed roller according to the thickness of the material passing between the pedals and the feed roller being averaged transversely of the machine by a special linkage and the resultant movement being used as a ,controlling signal for speeding up or slowing down the feed roller to even out the feed of material. More recently modifications to such a control system have been proposed in which control of short-term irregularities have continued to be effected in the manner described but in which a closed-loop system has been added, the purpose of which is to detect long-term changes in the regularity of the processed material and to cause a corresponding modification in the action of the open loop feed control.
Such control systems operate quite well in certain circumstances, for example in the case of a lap-fed scutcher, although suffering from certain disadvantages such as the necessity for the means sensitive to variation in thickness at the feed end of the machine to generate an inverse relationship for control purposes (that is to say, for an increase in thickness a reduction of feed is necessary, and vice versa). In other circumstances such systems suffer from serious short-comings. Thus, for example, in the case of a hopper-fed scutcher or card, a continued diminution of the supply of material from the hopper, as when it for some reason is becoming exhausted, merely leads to an increase in speed of the feed mechanism of the machine, which in turn aggravates the situation, the whole effect being cumulative and leading to a rapid and continued increase in the speed of the feed mechanism.
The object of the present invention is to provide means for controlling the regularity of material processed by machines of the type referred to which is efficient in operation and which substantially avoids the disadvantages hereinbefore set out.
According to the present invention a machine in which a property of a continuous length of material being processed thereby is modified, the modification depending upon the output characteristics of the machine relative to the input characteristics thereof, comprises means for continuously feeding material such as fibrous textile material thereto, means for continuously discharging said material therefrom, and adapted to modify a property such as the density or cross-sectional dimensions of said material during passage therethrough characterised by an openloop control means adapted continuously to produce a signal proportional to the actual value of the property ice to be modified of the material fed to the machine, and to alter, by varying said output characteristics, the modifying action of the machine on the material fed thereto in accordance with said signal to compensate for variations in said value, and a closed loop control means adapted continuosuly to produce a signal proportional at any time to the integral of variations in the value of the modified property of the material leaving the machine from a datum value with respect to time and to modify the signal produced by said open-loop control means in accordance With said integral signal in such a manner as will tend to reduce said variations from said datum.
The open-loop signal may be produced by suitably modifying a signal proportional to the value of some other property of the material fed to the machine, which is a function of the value of the property to be modified (e.g. the Weight per unit length may be the property to be modified, and the signal in this case may be proportional to the thickness of the material as it passes under a roller), and the closed-loop signal may be arranged to be such as suitably to modify the parameters of said modified signal.
The invention is particularly applicable to a machine which is adapted continuously to have fed thereto a fibrous textile material, continuously to modify the density of said material, and continuously to discharge said material in modified form, and especially such a machine in which the means for continuously discharging the material includes an output roller system, control of the Weight per unit length of the material being effected by Varying the speed of the latter. Such a machine (for example a scutcher) would preferably incorporate control means having the following features, namely:
(c1) Means for continuously producing a signal proportional to the input thickness T1 of the material fed thereto;
(b) Means for continuously producing a signal proportional to the speed V1 at which said feed roller system feeds material to the machine;
(c) Means adapted to receive the signal proportional to T1 and to transform it into a signal proportional to (T i) :51T 1ib 5 (d) Means adapted to receive the signals proportional to V1 and to f(T1) and to control the speed at which said output roller system discharges material from said machine (after a timed delay) if necessary at a value p, q, m and n being selected so that any error in the thickness of the material discharged from the machine causes a compensating variation of the speed of discharge of the output roller system. All such means will be described in greater detail.
The invention will no be described further, by way of example only, with reference to the accompanying drawings in which:
FIG. l is a diagrammatic representation of a scutcher with associated control means according to the invention;
FIG. 2 is a perspective View of part of the control means which is located at the output or front end of the scutcher;
FIG. 3 is a perspective view of another part of the control means located at the input or feed end of the scutcher, and
FIGS. 4 to 6 are circuit diagrams of certain of the electrical parts of the control means.
Reference will first be made to FIG. l.
The feed roller R1 of a scutcher S is driven at a nominally constant speed by a motor CSM. To take account of uncontrolled variations in the speed of motor CSM, the speed is measured by a tachorneter TA1 arranged to give an electrical signal proportional to the speed V1 of the input rollers R1.
Delivery rollers Ro (and also the cages and the means for forming the nished lap) of the scutcher S are driven by a variable speed motor VSM to which is coupled a tachometer TA2 arranged to give an electrical signal proportional to delivery roller speed V2.
Open-loop control of the regularity and uniformity of the material delivered by the scutcher S is effected by an input thickness transducer TR1, acting through a pedal system (FIG. 3) to give a signal proportional to the input thickness T1. To deal with (i) a known deviation in linearity between thickness of the material being fed and its superficial density and (ii) variations in the bulk modulus or compressibility of the material being fed, a function generator FG is used to transform the signal proportional to T1 into a signal proportional to f(T1)=aT1-b. This MT1) signal is fed to a motor speed controller MSC1 whose function is to maintain where T is the desired output thickness. This is facilitated by the subsidiary closed loop, shown in dotted line, through the tachometer TA2. An overall time delay in the action of this open loop control is not, in practice necessary, in view of the scutcher operating characteristics, but might well be necessary in other machines with long processing times. If, however, the transducer TR1 was disposed in advance of the feed roller system in a scutcher then a time delay would be necessary for this reason.
Closed loop control is through a transducer system TR2, measuring the error in input thickness, and giving a signal proportional to (T2-T) where T2 is the actual thickness of the delivery material. This signal is fed to another motor speed controller MSC2 which causes a servomotor SM to rotate at a speed proportional to (T2-T). To achieve accuracy in this a second subsidiary loop, shown in dotted line, is provided through a tachometer TA3, coupled to the servomotor SM and feeding back to motor speed controller MSC2. The final link in the closed loop is a mechanical coupling by shaft Sh between servomotor SM and function generator FG. As the speed of servomotor SM is at all times proportional to (T2-T) its angular position, and therefore, the angular position of the shaft Sh is dependent on the integral of this speed with respect to time, i.e. proportional toV f (T 2-T)dt. Thus a mechanical displacement proportional to f(T2-T)dt is fed to function generator FG,
permitting the modification of constants a and b so that at any time the values of p, q, m and n being so chosen as always to tend to reduce the error (T2-T).
By the system described it will be seen that the control effected by the motor speed controller MSC1 is in response partly to an open loop system capable of detecting shortterm Variations in the controlled property of the material and partly to a closed loop system capable of detecting long-term Variations of the controlled property and causes the functioning of the scutcher to be adjusted to cornpensate for both types of variation. Since the control is effected by varying the speed of the front or output rollers it is not necessary to generate in inverse relationship for control purposes, nor Will a gradual exhaustion of supply of material be aggravated in the manner previously mentioned, but on the contrary the output speed will be slowed down as much as necessary to compensate therefor.
Reference has been made in the foregoing description to motor speed controllers. Such devices are well-known in the electrical art. The motor speed controller MSC1 (which controls the speed of the variable speed motor VSM) and the motor speed controller MSC2 (which controls the speed of servo motor SM) may be of any suitable commercially available type. For example it could well be a Velodyne motor speed controller, in which a D.C. motor supplied with constant armature current has a degree of field excitation varied in accordance with the difference at any time existing between the voltage generated by a tachometer on the motor TA2 and a reference voltage (the demanded speed signal f(T 1)).
Reference will now be made to FIGS. 2 and 3 in order to describe in more detail certain of the mechanical features of the control system.
At the front or output end of the scutcher S are the usual calender rollers Ro and above the top calender roller 11 is disposed a pair of detectors 12 sensitive to the vertical position of the roller 11. Across the supporting framework 13 of the calender rollers is mounted a platform 14, and at each end of the latter, adjacent the bearings 11a of the calender roller 11 is a support 15. In each support 15 is pivotally mounted one end of a detector arm 16 which itself carries a transducer TR2 the sensitive portion Of which bears on a bar 18 supported by bearings 11a. Associated with the other end of each detector arm 16 is an adjustment and comparator means which Will not be described in detail herein,
Each transducer TR2 consists of a linear variable dilferential transformer comprising a suitably excited primary and a secondary output coil, with a common movable core forming the portion thereof sensitive to movement of the calender rollers caused by varying thickness of the material passing therebetween. The electrical output is proportional to the displacement of the core and thus to the thickness of the material coming from the scutcher. By arranging for the signal to be compared with a constant corresponding to T, the desired thickness, the signal T2-T is derived.
n At the feed or input end of the scutcher S the conventlonal pedal system 19 based on a piano linkage is modied for the purposes of the present invention. The final link 20 is adapted to operate the transducer TR1, which is also in the form of a linear variable differential transformer, whereby the signal T1 is derived.
The mainly electrical parts of the control system hereinbefore particularly described are shown in more detail in FIGS. 4 to 6.
FIG. 4 is a schematic circuit diagram of the function generator FG and its associated parts.
The output signal T1 from TR1 is converted to a direct current signal by a rectifier and filter E and is then amplified by a D.C. amplifier A1. To this signal is then added (i) A bias voltage derived from VA and developed across resistance R1 the magnitude of which is fixed by means of variable resistance RV1 and (ii) A bias voltage derived from VB and dependent upon f(T2-T) dt and developed across part of a servo potentiometer RVE, the movable arm of the servo potentiometer being driven by servomotor SM, the magnitude of which voltage is fixed by means of variable resistance RV2.
Adjustment of the magnitude of bias voltage derived from VA by means of RV1 corresponds to adjustment of the parameter m, and adjustment of the magnitude of bias voltage derived from VB by means of RV2 corresponds to adjustment of the proportionality constant n.
The total signal is fed into a second D.C. amplifier A2 through an input resistance R2 where the amplification is made dependent on f(T2-T) dt by having the other part of the servo potentiometer RVb in a feed back loop which also includes a variable resistance RV3.
Total amplification of the original signal T1 may then be expressed as p+qf(T2-T)df and the function parameters p and q can be set by adjustment of RV3 and RVb respectively. Thus the final output of the function generator FG may for practical purposes be expressed in the form:
FIG. 5 is a schematic circuit diagram of the motorised integrating system comprising the motor speed controller MSC2, the servomotor SM and the tachometer TA3.
This motor speed controller circuit to which signal T2-T is fed comprises a pre-amplifier A3 followed by an output amplifier A4 feeding into one coil of the bidirectional variable speed two-phase A.C. servomotor SM, the other coil being fed from a transformer through a phase correction network (not shown). The speed of the servomotor SM will be approximately proportional to the input signal of A2 but this latter part of the circuit is linearized by feeding back a signal from a drag-cup tachometer TA3 through a phase-correcting network PC then Where is the angular displacement of the shaft servomotor SM and K is a constant dependent upon the characteristics of the servomotor used and the gearing between the servomotor and the potentiometers of the function generator. The servomotor SM drives the servo potentiometer RVS., RVb (FIG. 4) through a gearbox GB with a slipping clutch (not shown) so that the movement of the potentiometer arm in time C #KL (T2-Tm FIG. 6 is a schematic circuit diagram of the system comprising the motor speed controller MSCl, the variable speed motor VSM and tachometer TA1.
The motor VSM is a 2 H.P. D.C. motor and the means for controlling its speed consists of a conventional full wave thyratron armature type of control.
The input signal f(T1) from the function generator FG is amplified by amplifier A and fed into the grid circuit GC of the thyratron. Feedback is provided by a precision D.C. tachogenerator PT for ensuring linear response and for minimising inherent drift in this part of the apparatus. Further feedbacks from E and F are designed to ensure maximum rates of response. These are cornbinde in the network circuit NC together with the signal V1 from tachometer TA1 for compensating for any drift in the speed of the feed roller R1.
Having now described in detail the construction and operation of our control apparatus as incorporated in a scutcher it will be readily understood that a much more accurate control of the regularity of the lap produced by the scutcher may be achieved thereby.
As is known the conventional piano-link control of a scutcher is itself a function generator in the sense in which the term is used in the present specification, but of a mechanical nature. Thus the pedal displacement corresponds to the thickness T1 of the incoming material and this displacement, for control purposes, is converted into f(T1)=aT1r-ib by the piano-link mechanism. The gain factor a is determined by the magnification effected by the linkage between the pedals, and the bias factor b is determined by the setting of the usual turnbuckle adjustment which is provided. It is current practice, and has been for many years, to fix the factor a by trial and error methods when first setting up the scutcher, whilst in use frequent adjustments are made to factor b as indicated by errors in the weight of the finished lap.
The necessity of using f(T1)=aT1-jb as a control function has been explained hereinbefore, for, as is implicit in that explanation, it is assumed that the relationship between the thickness and weight per unit length of the lap may be represented by a curve which is a straight line not passing through the origin. In fact of course the relationship is not linear, but for practical purposes may be considered so over the range of Variations which occur.
The conventional piano-link motion operates on the principle that the correct linear relationship may be selected by merely, in use, adjusting factor b-in other words that the slopes of the family of curves are all the same. In fact this is not so, and therefore, for more accurate control, factors a and b should be altered. The present invention provides for this, in the manner described hereinbefore. Thus the function generator of the present invention modifies both factors cz and .b in a manner indicated by the error in the delivered lap thickness to obtain a more accurately corrected function (aTl-j-b). Thus the main amplifier gain factor a and the bias voltage b are themselves generated by ancillary devices as function's of the error in delivered lap thickness (T2-T). Again it is convenient in each case to combine variable voltage and bias to produce an electrical signal of the required magnitude. In the preferred embodiment the integral of the error signal Litri-T) is obtained as the angular position of a motor shaft and this angular position is coupled mechanically to two electric potentiometers which provide the variable voltage components (Le. the q and n components of a and b respectively). The p and m components are provided by preset bias voltages determined by considerations similar to those involved in the determination of b. In practice thickness/weight per unit length curves are determined experimentally and the variables adjusted accordingly.
l. In a machine which so acts upon a continuous length of material fed to and through it that the value of a selected characteristic of the material is modified during the course of passage of the material through the machine, a control means which comprises:
(l) means for producing a first electric signal continuously proportional to the input value of said characteristic,
(2) means controlled by said signal for modifying the action of the machine to maintain a predetermined relationship between said input value and the corresponding output value,
(3) means for producing a second electric signal proportional to the integral, with respect to time, of deviations of said output value from a selected datum, and
(4) means controlled by said second signal for so modifying said first signal that said deviation is reduced.
2. A control means as defined in claim l, wherein said means (l) comprises- (i) a means for producing a signal proportional to the input value of a characteristic of the material other than that to be controlled, but a function thereof, and
(ii) means for modifying said last-mentioned signal.
3. A control-means as defined inclaim 2, wherein said means (4) is adapted to modify the parameters of the modified signal produced by means (ii).
4. A control means as defined in claim 1, wherein the material is a fibrous textile material and the machine is one which acts upon it to modify its density.
5. A control means as defined in claim 4, wherein the machine is a scutcher.
6. A control means as defined in claim 5, wherein the machine includes an input roller system and a variablespeed output roller system, andsaid means (2) modifies the action of the machine by Varying the speed of said output roller system.
7. A control means as defined in claim 6 having the following features namely:
(a) means for continuously producing a signal proportional to the input thickness T1 of the material fed thereto;
(b) means for continuously producing a signal proportional to the speed V1 at which said input roller system feeds material to the machine;
(c) means adapted to receive the signal proportional to T1 and to transform it into a signal proportional t0 (T1)=1T1+b;
(d) means adapted to receive the signals proportional to V1 and to (T1) and to control the speed at which said output roller system discharges material from said machine at a value and p, q, m and n being selected so that any error in the thickness of the material discharged from the machine causes a compensating variation of the speed of discharge of the output roller system.
References Cited in the file of this patent UNITED STATES PATENTS 2,531,644 Rayburn Nov. 28, 1950 2,981,986 Neil May 2, 1961 3,013,313 Catling et al Dec. 19, 1961