US3421710A - Unwinding apparatus - Google Patents

Description

Jan. 14, 1969 MIER 3,421,710

UNWIND ING APPARATUS Filed Sept. 27, 1966 Sheet of 4 earner fl: W 5; X 5L2 9 m/sm HIS/57095? I UNWINDING APPARATUS I Fi'led Sept. 27, 1966 Sheet 2 of 4 C [mm/c \j M0700 Jan. 14, 1969 G. MIER 3,421,110

UNWINDING APPARATUS Filed Sept. 27, 1966 Sheet of 4 Torque Speed 591.

Z z I 7)) Inventor Y n. l v a) //j/ 2? Y I Attorney Jan 14, 1969 MIER 3','-4' 21,71o-

UNWINDING APPARATUS Filed Sept. 27, 1966 Sheet 4 of 4 k, 5 K K a 3 Speed F/g' In uentor 7 h 1A b; 4 c

United States Patent ABSTRACT OF THE DISCLOSURE In controlling the tension of unwinding material, the pole wheel magnet brake is drawn in a direction opposite to that of a reel shaft at a speed which, with the reel shaft stationary, is sufiicient to reach the point of maximum torque, on the torque-speed characteristic, at the initial value of the brake coil current; thereafter, in the period between the commencement of unwinding and the attainment of full speed of the unwound material the brake coil current is regulated in accordance with the speed of the unwound material so that the current/ speed characteristic for the brake has a positive slope; and is made zero or negative.

The invention relates to apparatus for controlling the tension in the unwound material in unwinding arrangements employing an electromagnetic brake (induction or eddy-current brake) with an approximately hyperbolic torque-speed characteristic. It is desirable so to control the arrangement that the desired tensile stress of the strip material remains constant throughout the unwinding operation.

The problem posed in unwinding arrangements generally consists in obtaining as constant a tensile stress as possible irrespective of the winding diameter. Depending on the nature of the wound material and the manufacturing conditions, the degree of accuracy with which the tensile stress is to be maintained varies considerably.

Control arrangements for electro-magnetic brakes are known which efiect regulation to constant unwinding capacity and keep the tensile stress on the strip material constant at constant speed of the strip. On acceleration and deceleration, however, deviations from the desired strip tension occur. Such deviations are not permissible in many cases, in particular in the case of easily damaged strip material or when a large inertial mass is provided by the wound coil.

Furthermore, control or regulating arrangements for unwinders are known which measure the tensile stress of the strip material directly and use this quantity for regulation purposes. In these arrangements, the tensile stress is kept constant irrespective of the winding diameter and of acceleration and deceleration processes. However, the use of these strip tension measuring arrangements leads to additional expenditure for example for pressure-measuring capsules, tension adjusting rolls or pressure rollers which are additionally undesirable in many cases for reasons of space or because of special surface sensitivity of the strip material. Additionally, control arrangements for electromagnetic brakes are known which regulate strip tension by means of apparatus for mechanically or optically scanning the reel diameter. The drawback in these arrangements also resides in the additional expenditure on construction or in a certain hindrance in the operation of the machine. I

The present invention avoids this additional expenditure and the drawbacks associated therewith and nevertheless produces a substantially constant strip tension throughout the unwinding operation by employing electromagnetic brakes, known in themselves, of a kind having a torquespeed characteristic which after reaching a maximum torque as the speed increases from zero falls approximately hyperbolically. Direct measurement of the tensile stress and the winding diameter is deliberately avoided. According to the invention, the pole wheel of the brake is driven in a direction opposite to that of the reel shaft at a speed which, with the reel shaft stationary, is sufiicient to reach the point of maximum torque, on the torque-speed characteristic, at the initial value of the brake coil current; thereafter, in the period between the commencement of unwinding and the attainment of full speed of the unwound material the brake coil current is regulated in accordance with the speed of the unwound material so that the current/speed characteristic for the brake has a positive slope; and the current is then either maintained constant with increasing reel speed as the diameter of the wound material decreases, or the current is reduced as the reel speed increases. An electric signal derived from a tachometer connected to draw rollers for withdrawing wound material from the reel can be added to a constant signal and then used to control the brake coil current during the period of running up to full speed of the unwound material.

In order that the invention may be better understood, two examples of apparatus embodying the invention will now be described with reference to the accompanying drawings in which:

FIGURE 1 shows the circuit and arrangement of a first apparatus;

FIGURE 2 shows the circuit and arrangement of a second form of apparatus;

FIGURE 3 shows the torque-speed characteristic of the brake;

FIGURE 4 shows the coil-current/speed characteristic of the controlled brake;

FIGURE 5 illustrates the resistance curve for the acceleration and deceleration circuit;

FIGURE 6 shows the coil current/speed characteristic of the brake for the second form of apparatus.

The strip material is drawn from the winding-off reel 2 by the driving rollers 1. An electro-magnetic brake 3 (an eddy-current or induction brake) is connected to the reel shaft. It consists of two rotatably mounted halves, the socalled pole wheel 3a and the armature. The torque is transmitted by magnetic force and can be regulated by means of the current in the coil 4. The different values of current strength in the coil lead to a family of curves for the torque-speed characteristic of the electro-magnetic brake. These curves all have a form generally similar to that shown in FIGURE 3 and vary only by their ordinates, smaller values of the current corresponding to smaller values of torque. One half of the eddy-current or induction brake is coupled to the reel shaft and the other half is driven at constant speed in the direction opposite to the direction of wind-off by a geared three-phase electric motor 5. The speed is preferably so calculated that it is located at the turning point of the torque speed characteristic of FIGURE 3, in which the speed is the relative speed of the two brake parts. By turning point there is to be understood that point at which the upward convex curvature of the characteristic changes into an upward concave curvature. As a result, the steeply rising part of the characteristic as far as the turning point is avoided and only the part which is of an upward concave curvature and which is approximately hyperbolic is followed. It is not necessary for the speed to be exactly that required for the turning poin a smaller speed can be used provided that the point of maximum torque is reached; or a higher speed can be used, but it would not then be possible to use the full capacity of the brake.

The coil 4 is fed by an amplifier 6. The amplifier contains a current-regulating means which compares nominal and actual values and which ensures that the coil current is not alfected by the heating of the coil and the increase in the ohmic resistance that is associated therewith.

Rotary resistors 7, 8 and 9 are located in the input circuit of the amplifier 6. The rotary resistors 7 and 8 are mechanically coupled to one another and are adjusted to the initial winding diameter by means of a manually-operated rotary knob. The resistor 9 serves to adjust the desired winding tension and is connected in series with further resistors 10, 11, 17 and 18. The series-connected resistors 10 and 11 receive the sum of the voltage of a tachometer 12 and constant DC. voltage from a source 13. A tachometer 19 is connected across resistors 17 and 18. The tachometer 12 is mechanically coupled to the driving rollers 1 and its output therefore represents the linear speed of the unwound strip; the tachometer 19 is mechanically coupled to the reel shaft 2.

Even when the unwinding reel 2 is still at rest, there is already a relative speed between the two halves of the induction or eddy-current brake (due to the motor so that the tensile stress in the winding material between the driving rollers 1 and the reel 2 can be adjusted to the desired value with the reel stationary by means of the resistor 9.

If it is assumed that, when the unwinding arrangement starts up and until full speed of the strip is reached, the winding diameter decreases only to a negligible extent, the braking torque of the induction or eddy-current brake must remain constant in order to obtain a constant tensile stress. Without an adjustment to the current, the increase in relative speed speed of the two parts of the brake would cause a fall in torque. A constant torque shown as a dashed line parallel to the speed axis in FIGURE 3 can be achieved by causing the coil current (FIGURE 4) to increase from the value a adjusted at rest to the value b. To the value b of the coil-current corresponds the torquespeed characteristic of the brake represented by a full line in FIGURE 3. For the value a of coil-current there would be a lower curve (i.e. a curve having lower ordinates) which is not represented in FIGURE 1, and -for which the turning point is at the left-hand end of this dashed line parallel to the speed axis. Starting from this turning point for current a, the torque is prevented from decreasmg, as the speed increases, by the increase in current from a to b. The zero point of FIGURE 4 is displaced relative to FIGURE 3 so as to be at the abscissa of FIG- URE 3 corresponding to the turning point. The characteristic in accordance with which the adjustment of the coil current must take place can be determined point-by-point by graphic methods from the natural torque-speed characteristic of the electro-magnetic brake employed. A slightly curved characteristic (represented by the line a to b in FIGURE 4) is obtained, but it is possible to approximate this curve with sufiicient accuracy by a straight line. The manner in which the straight-line characteristic is obtained will be explained later.

After full speed of the strip has been reached, further unwinding should likewise take place at a constant tension and as the winding diameter is now decreasing at a greater rate, it is a factor which must be considered. The torque is obtained from the product of the tensile force and the winding radius and must therefore decrease to the same extent as the winding diameter. At constant strip speed, the result is a variation in torque in inverse ratio to the reel speed, i.e. in accordance with a hyperbola (shown by dashes in FIGURE 3). In order to achieve this, the coil current of the induction is made to decrease in dependence on the reel speed (FIGURE 4). The characteristic in accordance with which the coil current must be varied can likewise be determined point-by-point by graphic methods from the natural torque-speed characteristic of the electro-magnetic brake employed. An almost linear path is also obtained for this part of the current characteristic. In order to obtain the desired curve for the torque (shown in dashes in FIGURE 3), i.e. a constant braking torque during the run-up of the unwinder and a hyperbolically decreasing torque during unwinding at constant strip speed, the coil current of the induction brake must therefore first be made to increase in dependence on the strip speed and then downwards in dependence on the reel speed, in accordance with the angled characteristic of FIGURE 4.

This angled current characteristic is obtained by the differential connection of the two tachometers 12 and 19. The series-connected tachometer 12 and DC. voltage source 13 apply a voltage across potentiometer 10 and resistor 11 and the tapped voltage corresponds to the characteristic 1 (FIGURE 4). The DC. voltage is responsible for the initial value a of the coil current when the reel is at rest. On run-up, the tachometer 12 coupled to the driving rollers delivers a voltage which increases in proportion to the speed of the unwound strip and remains constant when full strip speed has been reached (characteristic 1, FIGURE 4). The tachometer 19, which is coupled to the reel shaft, delivers a voltage which increases in proportion to the speed of the reel. This voltage is applied across the series-connected resistor 17 and resistor 18 and the voltage tapped at the wiper of resistor 17 corresponds to the characteristic 2 of FIGURE 2. The negative ends of the resistors 11 and 18 are connected together. The difference between the two voltages tapped by the wipers of the resistors 10 and 17 is applied across the potentiometer 9 and controls the coil current in accordance with the angled current characteristic (FIGURE 4). This desired current characteristic is thus obtained by the difference of the two characteristics 1 and 2 (FIG- URE 4 The initial point a (FIGURE 4) and the slope of the current characteristic are also dependent on the initial diameter of the winding material. This effect is taken into consideration by the resistors 10 and 17. The fixed resistors 11 and 18 represent the smallest possible winding diameter, i.e. that of the reel mandrel or shaft.

On acceleration and deceleration of the unwinding arrangement, additional forces occur, these being dependent on the size of the inertial masses and the difference in speed per unit of time. It is assumed that the winding diameter can be regarded as a measure of the total inertial moment and that run-up and slowing down take place with constant acceleration and deceleration, respectively. On acceleration, the switch 24 closes and on deceleration the switch 25 closes. A DC. voltage is applied in each case across the series-connected potentiometers 7 and 8, the polarity depending on whether the switch 24 or 25 is closed, and the voltage between the wipers of these potentiometers varies the current supplied to the coil 4 by way of the amplifier 6 in such a manner that the acceleration and deceleration forces at the reel shaft are compensated. The sense of the correcting DC. voltage derived from the wipers of resistors 7 and 8 must be such that this voltage is deducted from the voltage tapped from the resistor 9 during acceleration, and is added to this latter voltage during deceleration. The switches 24 and 25 open again once the acceleration or deceleration has ended, these switches being controlled by acceleration and deceleration sensitive devices. FIGURE 5 shows an example of the varation of resistance required to compensate for acceleration forces in dependence on the reel diameter. The characteristic first has a negative slope but as the winding diameter increases, this changes to a positive slope. Such a characteristic is obtained when the inertial moment of the unwinding mandrel together with the mechanically coupled parts is sufliciently large, in relation to the inertial moment of the wound coil, not to be disregarded.

This characteristic can be approximated by giving the two mechanically coupled rotary resistors 7 and 8 a stepped winding such as to produce for each of them a resistance curve (shown in dashes in FIGURE 5) consisting of a number of linear portions of different slopes,

and by so connecting them electrically in series with their wipers moving in opposition that the sum of the two resistance value, during progressive adjustment of the angular position of the wipers first decreases and then increases again, so that the resistance curve desired for the required acceleration is obtained with good approximation. The resistor 26 is introduced because of mechanical friction; the frictional forces at the reel shaft have a braking action and the applied deceleration voltage value has therefore to be smaller than the acceleration voltage value.

The resistors 7, 8, and 17 are set to the initial diameter of the winding 0n reel 2 and then remain at this setting throughout the unwinding operation, unless for any reasons the unwinding is stopped before the strip is completely unwound. In such a case, these potentiometers would be reset to the new initial diameter.

The apparatus described above provides good compensation for the changing diameter of the would strip as unwinding proceeds. However, compensation to such a degree of accuracy may not in all cases be necessary and where this is so the simplified apparatus of FIGURE 2 may be used. This apparatus produces a coil current/ speed characteristic of the kind shown in FIGURE 6. It will be seen that in this case, once the unwound strip has attained full speed the coil current remains constant, the approximately hyperbolic torque-speed characteristic of the brake automatically providing some compensation for the effect, on the strip tension, of the decreasing winding diameter. As in the first case, the speed of rotation of the pole wheel of the brake is such that with the reel 2 stationary, the turning point of the torque-speed characteristic (or at least the point of maximum torque) is reached. In FIGURE 2, the tachometer 19 of FIGURE 1 is omitted together with the potentiometer 17 and the resistor 18 and the potentiometer 9 is supplied with the voltage between the wiper of the potentiometer 10' and the negative end of the resistor 11. The apparatus is in other respects similar to that of FIGURE 1. As a consequence of these changes, the voltage applied across potentiometer 9 varies only with the output of the tachometer 12, superimposed on the constant D.C. voltage from the source 13. This provides the angled current characteristic shown in FIGURE 6.

What I claim is:

1. Apparatus including an unwinding device having a reel for the material to be unwound and draw rollers for drawing the material from the reel, an eddy-current brake coupled to the reel shaft, means for rotating the pole wheel of the brake in a direction opposite to the direction of rotation of reel shaft, a tachometer connected to the draw rollers, a DC. voltage source connected in series with the tachometer, and a control circuit applying to the coil of the eddy-current brake a current which varies with the sum of the tachometer voltage and the DC. voltage source, in which the control circuit for the coil of the brake includes an adjustable resistance to be set in accordance with the intial diameter of the wound material on the reel, the adjustable resistance being connected to the constant DC voltage source through a reversing switch which is closed in one sense during acceleration and in the opposite sense during deceleration of the reel, the deceleration circuit including an additional resistor.

2. Apparatus in accordance with claim 1, in which the said adjustable resistance comprises two resistors, both set in accordance with the initial diameter of the wound material, the two resistors being contoured to provide a non-linear resistance variation and having their wipers connected in mechanical opposition so that the sum of their resistances, plotted against the diameter of the wound material, first decreases in non-linear manner as the diameter is reduced and then increases, to provide the required acceleration characteristic.

3. An arrangement for maintaining substantially constant the tension in the wound material in an unwinding device including a reel for the material to be unwound and draw rollers for drawing the material from the reel, an eddy-current brake coupled with the unwinding shaft and having a torque speed characteristic which after reaching a maximum torque falls approximate-1y hyperbolically with increasing slip, a motor for driving the pole wheel of the brake in a directon opposite to that of the reel shaft, a tachometer connected to the draw rollers, a AC. voltage source connected in series with the tachometer, a plurality of resistors, and wipers therefor in which (a) the free ends of the DC. source and the tachometer connected in series are connected to the ends of a first one of said resistors which (b) is connected by one of its ends and by its 'wiper with both ends of a second resistor, and

(c) one end of the second resistor and its wiper are connected across an amplifier with the winding of the brake pole wheel.

4. Arrangement according to claim 1 in which there is provided a second tachometer coupled with the unwinding shaft and connected to the ends of a third resistor which is inserted by one of its ends and its wiper in the connection between the first resistor and the second resistor, whereby the voltage of the second tachometer is opposed to the sum of the voltages produced by the first mentioned tachometer and the D0. source.

5. Arrangement according to claim 1 in which for the compensation of the acceleration and deceleration forces two further resistors arranged in series are provided for the connection of the second resistor and the amplifier, there are provided wipers for said further resistors, and two switches, and a further D.C. source, the further resistors are connected at their free ends with said further D.C. source across two switches for pole changing.

6. Arrangement according to claim 3, in which a resistor is inserted in series with the further resistors and the switch to be closed at deceleration.

7. Arrangement according to claim 3, in which the further resistors are contoured to provide a non-linear resistance so that the sum of their resistances as picked up by their wipers mechanically connected with another, plotted against the diameter of the wound material, first decreases in a non-linear manner as the diameter of the supply reel is reduced and then increases, to provide the required acceleration characteristic.

8. Arrangement according to claim 3, in which the wipers of the resistors (7, 8, 10 and 17) are mechanically coupled and simultaneously adjustable whereby the windings of the potentiometers are accorded with each other in order to furnish the desired resistance values for each position of the wipers.

9. Arrangement according to claim 1, in which each of the first and third resistors consist of two parts, one of them representing diameter of the core on which the material is wound and the other being adjustable in function of the initial diameter of the material wound on the core.

References Cited UNITED STATES PATENTS 2,469,706 5/1949 Winther 1 .42-75.51 2,917,252 12/ 1959 Bushnell et a1. 242-75.47 3,049,313 8/1962 Jordan et a1. 242-75.44 3,257,086 6/ 1966 Drenning 24275.47 X

FOREIGN PATENTS 544,925 5/ 1942. Great Britain.

FRANK I. COHEN, Primary Examiner.

N. L. MINTZ, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,421,710 January 14, 1969 Gerhard Mier It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 31, cancel "speed", second occurrence. Column 4, line 27 "resistors" should read Potentiometers line 28, potentiometef should read resistor Column 5, line 3, "value" should read values line 14, "reasons" should read reason line 18, "would" should read wound Column 6, line 11, "A.C. should read D.C. line 22, claim reference numeral "1 should read 3 line 30, claimre'ference numeral 1'' should read 3 line 38, claim reference numeral "3" should read S line 41, claim reference numeral "3" should read 5 line 49, claim'reference numeral "3" should read 5 line 55 claim reference numeral "1" should read 4 Signed and sealed this 17th day of March. 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer

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