GB2062037A

GB2062037A - Regulating the cross-section of the fiber roving delivered by a drawing machine

Info

Publication number: GB2062037A
Application number: GB8030972A
Authority: GB
Original assignee: Alsacienne de Constructions Mecaniques SA
Current assignee: Alsacienne de Constructions Mecaniques SA
Priority date: 1979-09-27
Filing date: 1980-09-25
Publication date: 1981-05-20
Also published as: FR2466526B1; IT8024964A0; DE3036446A1; FR2466526A1; IT1132781B; CH642404A5

Abstract

The drawing rollers (3) and the small rollers (5) for guiding the roving delivered by a textile fiber drawing machine are driven by a main shaft (5a). The feeding rollers (1) are driven from the same shaft through a differential mechanism (14) coupled to an auxiliary motor (30) which is controlled by an electronic speed- changing unit (29). This unit is responsive to the difference between voltages delivered respectively by a tacho-dynamo (31) which is driven by the auxiliary motor and by an electronic memory (28) placed at the output of a strain-gauge bridge (27). The bridge is influenced by strain gauges (26) fixed on resilient feeler blades (25) which are applied against the fiber slivers (2a, 2b, 2c, 2d) by means of wheels (23, 24). Any increase in sliver thickness sensed by the strain gauges produces a reduction in speed of the feeding rollers and a corresponding increase in the degree of draft. Conversely, a reduction in sliver thickness has the effect of increasing the roller speed and reducing the degree of draft. <IMAGE>

Description

SPECIFICATION An installation for regulating the cross-section of the fiber roving delivered by a drawing machine This invention relates to the textile industry and more particularly to machines for drawing-out fiber slivers. To explain the general principle of operation in very broad outline, a drawing machine is supplied with a certain number of card slivers (usually eight) which are rolled and drawnout together by passing between a certain number of pairs of rollers in order to form a fibrous mass, said mass being recondensed in a more compact sliver or rove which is coiled in a can. This rove serves to supply roving frames, free-fiber spinning frames and so forth. The quality of the yarn delivered by these machines is in close dependence on the uniformity of the fiber roving which is introduced at the feed end.It is consequently an advantage to ensure that the cross-section of the product delivered by a drawing device is as constant as possible.

Installations for maintaining a constant crosssection of roving delivered by machines for drawing-out textile fibers are already known, for example as disclosed in French patent No.

1 ,1 06,188. An An installation of this type comprises a pair of feeding rollers and at least one pair of drawing rollers, one of the two pairs of rollers being coupled directly to a main shaft driven by a main motor, the other pair of rollers being coupled to the same main shaft through the intermediary of a first element of a differential mechanism, a second element of said mechanism being coupled to the main shaft and a third element being coupled to an auxiliary motor which is supplied under the control of an electronic speed-changing unit. The input of said unit is connected to a device for comparison of a first voltage delivered by a tacho-dynamo driven at a speed which is a function of the speed of the drawing rollers with a second voltage delivered by means for measuring the thickness of fiber roving.

However, in known installations of this type, the pair of rollers which is coupled to the main shaft through the intermediary of the differential mechanism (namely that pair of rollers whose speed is subjected to variations under the action of the regulating process) is precisely the pair of drawing rollers. However, this arrangement is attended by disadvantages by reason of the fact that the trains of drawing rollers have relatively high inertia, with the result that the differential mechanism and the auxiliary motor must be of unduly large size and that the speed-regulating response time can be considered excessive.

The primary aim of the present invention is to overcome this disadvantage. With this objective, in accordance with a first distinctive feature of the invention, that pair of rollers which is coupled to the main shaft through the differential mechanism is the pair of feeding rollers. By reason of the fact that the inertia of the feeding rollers is much lower than that of the rollers of the drawing train, the advantage of this arrangement can readily be understood.

Moreover, in known installations of the type which has just been recalled, the means for measuring the thickness of fiber slivers comprise a wheel which is adapted to run on the sliver and is carried by a rocker-arm for actuating the slider of a potentiometer. In point of fact, the operating speed of a mechanical system of this type is clearly very low and produces response times of unacceptable length for present-day drawing machines in which the slivers of textile fibers attain speeds of the order of 600 m/minute.

The present invention has the further object of overcoming this second disadvantage. To this end, the means for measuring the thickness of slivers are constituted by a runner-wheel which, in accordance with known practice, is applied elastically against a fiber sliver opposite to a wheel located in a stationary position and carried by a blade spring on which are fixed strain gages connected to a strain gage bridge. A system of this type introduces practically no delay in the measurement and the variations in voltage produced by the strain gage bridge can be utilized by an electronic speed-changing unit having an extremely short response time.

Further distinctive features and advantages of the invention will become apparent from the following description and from the accompanying drawings in which one embodiment of the invention is shown by way of example and in which: Fig. 1 is a schematic illustration of a machine for drawing textile fiber slivers; said machine being equipped with an installation in accordance with the invention for regularizing the cross-section of the fiber roving delivered by the machine; Fig. 2 is a perspective view showing the detail of a particular embodiment of a feeler for measuring the thickness of fiber slivers which pass into the machine; Fig. 3 is a schematic view showing the operation of the memory or storage device; Fig. 4 is an experimental curve of the transfer function between the variation in thickness of card slivers and the variation in speed of the feeding rollers of the drawing machine; Fig. 5 is a block diagram of the electronic speed-changing unit; Fig. 6 is a simplified diagram of the power stage of the electronic speed-changing unit; Fig. 7 is a simplified diagram of a device for limiting the motor-braking current.

The drawing machine shown diagrammatically in Fig. 1 comprises a pair of feeding rollers 1 (the bottom roller is concealed by the top roller in the figure) between which are engaged in known manner a certain number of card slivers 2a, 2b, 2c, 2d. As a general rule, these slivers are eight in number. After passing between the feeding rollers 1, said slivers are introduced into the drawing train, only the last pair of rollers of said train being shown in the figure at 3. The layer 4 of fibers penetrates into a funnel (not shown), the outlet of which is constituted by the interval between two small rollers 5 whose function is to condense the layer 4 into a fiber rove 6 which is coiled in known manner within a can (not shown in the drawings).

The small roller 5 is rigidly fixed to a main drive shaft 5a driven by a main motor m which causes the rollers 3 of the drawing train to rotate by means of pinions 7,8 and a splined drive belt 9. A pinion 10 rigidly fixed to the pinion 7 drives a pinion 12 by means of a splined belt 11, said pinion 12 being rigidly fixed to a sun gear 13 which is loosely mounted on the central shaft 17 of a differential gear unit 14. By changing the pinion 12, the differential gear unit 14 can be adapted to drawing machines having a different output speed.The central shaft 1 7 is rotatably mounted in two stationary bearings 1 7a, 176 and carries a disk 32 which is mounted to rotate freely on said shaft and the rim of which forms a toothed ring 39 for receiving a splined belt 40 to which further reference will be made hereinafter. Two planetary pinions 33, 34 are rigidly fixed to a freely rotatable shaft 35 which extends through the disk 32. Said planetary pinions are coupled respectively by means of two splined drive belts 37, 38 to the first sun gear 13 and to a second sun gear 1 5 which is rigidly fixed on the central shaft 17.A toothed pinion 16 Fixed on the central shaft 1 7 drives the feeding rollers 1 by means of a drive system comprising a splined belt 18, a toothed pinion 19, a toothed pinion 20 keyed on the same shaft 1 9a as the pinion 19, a splined belt 22 and a toothed pinion 21 rigidly fixed to one of the feeding rollers 1. The characteristics of this drive system determine the degree of draft. This value can be modified, for example by replacing the pinions 16 and/or 19 by other pinions having different numbers of teeth since the speed of the feeding rollers 1 is thus caused to vary with respect to the speed of the drawing rollers 3.

A differential drive of the same type as the differential gear unit 14 described in the foregoing has been disclosed in French patent Application No. 79 23 395 entitled "Differential mechanism" and filed by the present Applicant on September 20th, 1 979. For further details, reference may usefully be made to this patent specification.

Before engaging between the feeding rollers 1, the card slivers 2a, ..... . pass between two feeler wheels 23, 24. The first wheel (23) occupies a fixed location whereas the second wheel (24) is capable of moving either towards or away from the first to a slight extent. Said second wheel is mounted on a blade spring 25 (also shown in Fig. 2) which is adapted to carry a strain gage 26 and this latter is connected to a strain gage bridge 27 of any suitable and conventional type which is capable of delivering a voltage having a value which is a function of the instantaneous condition of the strain gage.When a variation occurs in the thickness E of the mass of fibers while this latter is passing between the wheels, the wheel 24 undergoes a displacement and the strain gage senses this displacement, thus producing a variation in output voltage of the strain-gage bridge. As shown in Fig. 2, the device is made more sensitive if provision is made for one strain gage per card sliver instead of a single gage or, better still, if provision is made for two strain gages such as those designated by the references 26a and 26b and fixed respectively on two opposite faces of the spring blade which carries said gages so as to monitor each card sliver.The information derived from the feeler wheels 23, 24 or in other words the value of the output voltage of the strain-gage bridge 27 must be utilized at the moment when the cross-section of the mass of fibers which has just been measured reaches the drawing zone located between the feeding rollers 1 and the drawing rollers 3. This zone is in fact located at a distance of approximately 0.60 m from the feeler wheels 23, 24. The fiber transit time over this distance is not negligible and is in any case variable as a function of the degree of draft.

In order to delay the signal by a period equal to the fiber transit time, said signal is stored in memory at 28. Since a given drawing machine is capable of processing fibers of different lengths, a margin must accordingly be provided. This has been achieved by considering two fiber transit distances: one is the distance between the feeler wheels 23, 24 and the feeding rollers 1 , the other is the distance between the feeler wheels 23, 24 and the last train 3 of drawing rollers. A system which operates between these two limits is satisfactory in all cases. If the distance between the feeler wheels and the last drawing train is of the order of 0.75 m and if it is desired to utilize information relating to each centimeter of sliver, the number of data to be stored in the memory 28 will be of the order of 75.

Shift-register storage devices are well-known but are very costly for capacities of this order. It is for this reason that a random access memory 100 is employed in this instance (as shown in Fig. 3).

Considering the capacity of these memories, it has been decided to write 128 data over a length corresponding to the distance between the feeler wheels and the feeding rollers 1 (0.55 m in the machine considered). This results in approximately one item of information or datum at intervals of 4.28 mm (instead of intervals of 26 mm in the case of a conventional mechanical storage device). Whenever it proves necessary to consider the transit distance up to the entrance of the drawing train, it will only be necessary to add about forty data. In order to simplify control of the machine, the number 128 is programmed in advance and only the additional pulses are displayed when required by means of two coding wheels: one wheel for the units and one wheel for the tens. This latter is blocked below 0 and above 3, thus permitting easy and rapid display of whole numbers from 00 to 39. Since the distance between the stored data is constant, the time which elapses between two consecutive data depends on the speed of rotation of the feeding rollers. It is this elapsed time interval which controls storage of data relating to the thickness E of the fiber sliver. The angular velocity transducer is constituted by a disk 101 in which are formed uniformly spaced peripheral notches 102 and which is driven in rotation by the feeding rollers 1.

Said disk rotates in front of an oscillator 103 which stops in the presence of a metallic component. The signal emitted by said oscillator is therefore chopped so as to produce pulses corresponding to the notches 102 formed in the periphery of the disk 101. Since the diameter of the feeding roller 1 is 0.060 m and the data spacing is 0.00428 m, the disk has: n = 7r .0.060/0.00428=44 notches.

At each pulse delivered by the angular velocity transducer, a known electronic circuit 104 initiates writing of an item of information or datum in the memory 100. When the desired number of data in respect of one revolution of the feeding rollers 1 has been recorded in the memory 100, the pulse counters decrement by one unit each time the notch transducer undergoes a displacement through one forty-fourth of a revolution and a datum is extracted from the memory in order to control the speed of rotation of the feeding rollers 1 in the manner which will be described below. At the end of the cycle, the counters are automatically reset in the starting position.

The type of memory provided starts from a fixed interval (4.28 mm) between the data relating to the thickness of the fibrous mass which passes between the feeding rollers. As can readily be understood, it would be possible to start from a fixed number of data on the velocitypickup/drawing distance. A variation would accordingly take place in the interval between data in order to take into account the different lengths of fibers being processed.

The signal delivered by the memory 28 constitutes a velocity reference voltage and is transmitted to a four-quadrant electronic speedchanging unit 29 which supplies direct current to an auxiliary motor 30. Said motor preferably has low inertia and therefore very short acceleration and braking times, thus resulting in very fast reversals of the direction of rotation. A motor of the "Axem" type having a printed rotor and permanent-magnet excitation produces good results. Its speed is indicated by a tacho-dynamo 31, the output voltage of which is compared with the reference voltage delivered by the memory 28, the speed of rotation of the motor 30 being corrected as a function of the difference between the reference voltage and the effective voltage of the motor.The shaft 42 of the motor 30 carries a toothed pinion 41 over which is passed a splined belt 40 for driving the toothed ring 39 of the differential gear unit 14.

Considered as a general class, electronic speedchanging devices or regulators are well-known and commonly employed in industry. Among those which are commercially available, not one of these devices is adapted to the very special application contemplated in the present invention.

In particular, the response times are much too long. It is essential on the one hand to ensure that the supply of the motor is based on the principle of pulse-width modulation and on the other hand to ensure that the regulator is of the proportionalintegral type with a transfer function of the form G(p) = l/p. In fact, Fig. 4 reproduces an experimental determination of the transfer function N = f(E) in which the variation in speed of the motor is related to the variation in thickness of the fiber sliver which passes into the machine. It is established that this curve is a hyperbolic arc representing a homographic function of the form y= 1/x.

These two characteristics are found in the "Axodyn" speed-changer manufactured by the Company known as C.E.M. ("Compagnie Electromecanique"). In the first place, however, this device has an excessively long response time and consists in the second place of a onequadrant speed-changer which therefore does not permit rotation of the motor in both directions.

There does exist one embodiment of the invention which permits the use of a speed-changer of this type but its disadvantages will be explained hereinafter. It is for this reason that the preferred embodiment makes use of a specially-constructed four-quadrant speed-changer.

Fig. 5 is a block diagram illustrating this speedchanging unit. The reference voltage derived from the memory 28 and the output voltage of the tacho-dynamo 31 are applied to a comparator 200 (known per se), the output voltage of which is a function of the difference between the input voltages. Said output voltage of the comparator 200 is applied to a proportional-integral regulator 201 (also known per se), the output signal of which drives both an absolute-value detector 202 and a sign detector 203. The output signal of the absolute-value detector 202 serves to modulate the width of the pulses from which the supply current of the motor 30 will be obtained and the output signal of the sign detector 203 determines the direction of rotation of the motor 30.

Adaptation of the supply by pulse-width modulation to a motor which is capable of rotating in both directions has presented a slight problem.

For each direction of rotation, provision is made for two power transistors mounted in a Darlington circuit. At the moment of reversal of the direction of rotation, the four transistors are in the conducting state and this results in a short-circuit over a brief period. It has proved necessary to introduce a deliberate time-delay in turn-on of the two transistors which had not been caused to conduct until the first two transistors were no longer in the conducting state. Immediate reversal of the direction of rotation of the motor is therefore not possible. This has led to the need to seek a compromise between a permissible timedelay and the need to protect the transistors against this short-circuit.Moreover, the response time of a conventional Darlington circuit is too long and a p-n-p transistor is accordingly inserted in the circuit in order to reduce this response time, with the result that the switching time is much faster. Fig. 6 illustrates the power stage represented schematically at 205 in the block diagram of Fig. 5. The transistors 300 and 301 supply the motor 30 when this latter rotates in one direction and the transistors 302 and 303 supply the motor when it rotates in the other direction. The transistors 304 and 305 are of the pnp type and are intended to reduce the switching time in accordance with the invention. When the motor is slowed-down, it behaves as a generator and returns current into the transistors which are highly liable to be damaged.This disadvantage is removed at the moment of braking by placing a resistor 306 at the supply voltage terminals of the motor. Braking is initiated by the voltage collected at A in the resistor bridge 307, 308. A signal returned by the braking device (known perse) is applied at B, thus triggering the transistor 309 into conduction and connecting the resistor 306 in parallel with the motor supply. It is this resistor which "absorbs" the current delivered by the motor and not the transistors 300, 301, 302 and 303.

Moreover, the braking current is limited by a device designated by the reference 206 in Fig. 5 and having the function of comparing the current emitted by the motor and measured at 207 with a current reference 208. The device 206 is shown in Fig. 7.

The photocouplers 311 and 312 measure the voltage drop at the terminals of the resistor 31 0 which is in series with the motor 30. Two photocouplers are required since the motor is capable of rotating in both directions and the current passes through the resistor 310 in both directions. Conduction of the phototransistor 313 is a function of the illumination of the diodes 311 or 312. The voltage resulting from this photoconduction is applied to the integrator 314, the output signal of which is compared with a current reference applied at F. If the measurement is higher than the reference value, the AND-gate 31 5 which also receives at G the output of a current comparator reverts to the non-conducting state and the limitation is operative. Conversely, if the measurement is below the reference value, the limitation is not put into operation.

In the block diagram of Fig. 5, the current reference is designated by the numeral 208, measurement of the current by the photocouplers is designated by the numeral 207 and the current limitation is shown at 206.

The general operation of the system is as follows: In the stationary state, the textile fiber slivers 2a, 2b, 2c, 2ddo not cause any displacement of the feeler wheel or wheels 24, with the result that the memory 28 does not record any voltage variation at the output of the strain-gage bridge 27 and that the electronic speed-changing unit 29 is in the inoperative state. The motor 30 is stopped, with the result that the planet-wheel carrier disk 32 of the differential gear unit 14 is also stopped, that said unit operates simply as a planetary reduction-gear unit and that the speed of the feeding rollers 1 is not subsequently modified.

If the thickness of one or a number of fiber slivers undergoes a change and increases, for example, the corresponding feeler wheels 24 are downwardly displaced to a slight extent, the strain gage 26 modifies the conditions of the strain-gage bridge 27, the variation in output voltage of the bridge is injected into the memory 28 which stores said variation during a time interval equal to the transfer time mentioned earlier, whereupon this information is sent to the electronic speedchanging unit 29 which initiates the supply of the motor 30 with a polarity corresponding to the sign of the voltage received.In consequence, the motor rotates in the direction which produces a reduction in speed of the sun gear 1 5 of the differential unit 14, thereby causing a reduction in speed of the feeding rollers 1 and a corresponding increase in the degree of draft of the thickest portion of the slivers in order to ensure that the thickness of the roving 6 delivered by the drawing rollers 3 remains constant. The tacho-dynamo 31 is driven by the motor 30 and delivers a voltage which is placed in opposition, within the speedchanging unit 29, with respect to the voltage delivered by the memory 28. The speed of the motor is stabilized from the instant at which these two voltages are balanced and the installation continues to operate under the same conditions as long as no further change takes placed in the thickness of the roves which are delivered.

Conversely, a temporary reduction in thickness of supplied slivers would produce an increase in speed of the feeding rollers as a result of inverse reactions of the installation and this would have the effect of reducing the degree of drawing of the thinnest portions of sliver.

By way of alternative, the electronic speedchanging unit 29 could be of the single-quadrant type. In this case, the auxiliary motor 30 would continue to rotate in the same direction at a speed which is variable as a function of the conditions of the regulating system in response to the signals delivered by the feelers 24; the planet-wheel carrier disk 32 of the differential unit 14 would never be stationary. The speeds of rotation of the different elements could attain much higher values, thus entailing the use of a motor 30 having a much higher power rating in order to overcome the forces of inertia resulting from the increase in speed.

In all cases, the regulating device described in the foregoing also has the advantage of again ensuring constancy of thickness of the fiber roving 6 delivered by the machine when the speed of the drawing-roller train is different from its nominal speed, namely at start-up of the machine, or during slowing-down prior to stoppage or else after a roving breakage. Without a regulating operation of this type, a major flaw affects the emergent roving each time the speed of the drawing-roller train undergoes a variation.

Another distinctive feature lies in the fact that a tacho-dynamo 43 is added to the installation and driven by the main motor m, the output voltage of said tacho-dynamo being also transmitted to the electronic speed-changing unit 29. Under these conditions, the speed of the feeding rollers 1 can also be adjusted as a function of the speed of the drawing-roller train 3 which may be considerably lower than its nominal speed.

In accordance with a further distinctive feature, the value of the degree of drafts can be varied without entailing the need to change at least one of the two toothed pinions 16 and 19. This is achieved by coupling a tacho-dynamo 44 to the pinion 1 6 which controls the drive to the feeding rollers 1 and by injecting the output voltage of said tacho-dynamo into the electronic speed-changing unit 29.

Claims

1. An installation for regulating the cross section of the fibre roving delivered by a textile fibre drawing machine comprising a pair of feeding rollers and at least one pair of drawing rollers, one of the two pairs of rollers being coupled directly to a main shaft driven by a main motor and the other pair of rollers being coupled to the same main shaft through a first element of a differential mechanism, a second element of the said mechanism being coupled to the main shaft and a third element being coupled to an auxiliary motor which is supplied under the control of an electronic speed-changing unit, the input of the said unit being connected to a device for comparison of a first voltage delivered by a tacho dynamo driven at a speed which is a function of the speed of the drawing rollers with a second voltage delivered by means for measuring the thickness of the fibre roving, wherein: - the pair of rollers which is coupled directly to the main shaft is the pair of drawing rollers; - the pair of rollers which is coupled to the main shaft through the differential mechanism is the pair of feeding rollers; - the tacho-dynamo for delivering the said first voltage transmitted to the comparison device is connected directly to the auxiliary motor; - the said second voltage is transmitted to the electronic speed-changing unit via an electronic memory.

2. An installation in accordance with claim 1, wherein the means for measuring the thickness of roving comprise strain gauges carried by spring blades and connected to a strain-gauge bridge.

3. An installation in accordance with claim 2, wherein each spring blade is adapted to carry on two opposite faces two strain gauges connected electrically in opposition.

4. An installation in accordance with claim 1, wherein the said first elements of the differential mechanism are two sun gears and the third element of the said mechanism is a planet-carrier disc.

5. An installation in accordance with claim 1, wherein the coupling between the first element of the differential mechanism and the feeding rollers is constituted by a variable-ratio drive system consisting for example of interchangeable toothed pinions having different diameters so as to permit modification of the degree of draft.

6. An installation in accordance with claim 1, wherein the voltage delivered by a tacho-dynamo driven by the main motor m is also transmitted to the electronic speed-changing unit in order to control the speed of the feeding rollers in dependence on the speed of the drawing-roller train.

7. An installation in accordance with claim 1, wherein the voltage delivered by a tacho-dynamo driven by the said first element of the differential mechanism is also transmitted to the electronic speed-changing unit in order to permit a modification of the degree of draft.

8. An installation in accordance with any one of claims 1 to 7, wherein the supply of the auxiliary motor is effected in accordance with the principle of pulse-width modulation but with additional amplifying means for reducing the switching time.

9. An installation in accordance with claim 8, wherein the said installation comprises means for intentionally delaying reversal of the direction of rotation of the auxiliary motor, the said delaying means being adapted to prevent short-circuiting of the supply at the moment of switchover.

10. An installation in accordance with claim 1, wherein the transfer function of the regulator of the electronic speed-changing unit reproduces the transfer function of the variation in speed of the auxiliary motor with respect to the variation in thickness of the fibre sliver.

11. An installation in accordance with claim 1, wherein the electronic speed-changing unit is of the four-quadrant type.

12. An installation in accordance with claim 1, wherein a resistance circuit is connected in parallel with the auxiliary motor so as to protect the power stage of the electronic speed-changing unit by absorbing the energy released by the motor at the moment of braking of the said motor.

1 3. An installation in accordance with claim 12, wherein the braking current limiter is equipped with photocouplers.

14. An installation for regulating the crosssection of fibre roving delivered by a textile fibre drawing machine. substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.