GB2216503A - Controlling roll drive in unwinding apparatus - Google Patents

Description

CONTROL MEANS FOR CONTROLLING ROLL DRIVE IN ROLL UNWINDING APPARATUS The present invention relates to control means for controlling roll drive in apparatus for unwinding rolls of web material, especially in a rotary printing machine.

In roll unwinding equipment with automatic roll change, the required time for the acceleration of a replacement roll from zero to web speed is needed for, inter alia, determining instants of initiation of roll change stews. This time is preset in one known control means (DE-PS 26 19 236). However, the required acceleration time should however be determined as accurately as possible for the following reasons: In the case of an acceleration time which is too large, the replacement roll accelerated to the web speed of the printing machine carries out additional revolutions until elapsing of this time. This increases the risk that the adhesive tip prepared for the adhesion detaches from the roll and a faulty gluing takes place or the roll change operation must be stopped and gluing carried out by hand.If the required acceleration time is thereagainst greater than that provided, the gluing operation following the acceleration is initiated belatedly, which can have the consequence that the remainder of the web on the old roll is used up before the gluing is carried out and thus the automatic gluing operation fails. In all cases, machine standstill and printer's waste result.

Knowledge of the moment of inertia of the replacement roll is also advantageous in roll unwinding equipment. According to EP application 18 555, this is calculated from the measured time for the acceleration of the replacement roll to web speed. In that case it is disadvantageous that the moment of inertia is not yet available for the achievement of a regulated braking moment of the replacement roll in the event of braking to a stop during the acceleration process. Thus, the adhesive tip in the case of equipment with belt drives and the sleeve at the cone in the case of equipment with a central drive is greatly loaded, during braking to a stop of a small roll, by an unnecessarily high braking moment. In the first case, displacement of the adhesive tip may occur and faulty gluing as a consequence.In the second case, damage of the spool sleeve may occur and this requires further printing at reduced web speed or even replacement of this roll with consequent interruption of printing. It is also disadvantageous that the acceleration of the replacement roll-takes place at constant torque. In the case of a small replacement roll, the adhesive tip is heavily loaded, which can lead to lifting off of the tip with the already mentioned consequences.

There is therefore a need for roll drive control means which may remove or reduce the likelihood of faulty gluing and thus reduce printer's waste and machine standstill time.

According to the present invention there is provided control means for controlling roll drive in apparatus for unwinding rolls of web material, the control means comprising drive means for a replacement roll of web material, a speed controller to provide a control value for controlling the driving speed of the drive means, regulating means to regulate the speed controller, actual value determining means to determine the actual values of rotational speed of the replacement roll, circumferential speed of the replacement roll and speed of movement of the web material withdrawn from a further roll being unwound, storage and processing means for storing and processing the determined actual values and the control value, target value determining means to determine a target value for tangential acceleration of the replacement roll, the target value determining means being connected to the storage and processing means, differentiating means to differentiate the actual value of circumferential speed of the replacement roll for determining the actual value of tangential acceleration of the replacement roll, and comparison means to compare the actual and target values of tangential acceleration and to control the regulating means in dependence on the comparison result.

In a preferred embodiment, the control means serves for controlling acceleration of a replacement roll and comprises a regulated drive for the replacement roll, a measurement value transmitter for its circumferential speed, a computer and storage unit which is fed with measurement values for the circumferential speed and rotational speed of the replacement roll, a measurement value transmitter for the web speed, and a regulating device with a rotational speed controller which is connected to the output thereof and which is connected with a control member of the drive, the control means being operable to ensure timely determination of the acceleration time of the replacement roll as well as its moment of inertia and to preserve an adhesive tip of the roll.The measurement value transmitter for the circumferential speed of the replacement spool roll feeds a differentiating member which at the output side is connected with an actual value input of a comparison member, a target value input of which is connected with a target value generator and the output of which is connected with the regulating device. A current transformer in the current path of the setting member of the drive and the target value transmitter are connected to the computer and storage unit.

With this control means, the replacement roll is accelerated, independently of its size or moment of inertia,with a preselectable constant tangential acceleration. This makes it possible to calculate exactly the required acceleration time of the particular replacement roll at the desired instant in time in order to attain the prevailing web speed of a downstream processing machine, for which purpose a very simple mathematical relationship is used. The acceleration time thus determined permits the commencement of acceleration.of the replacement roll to be fixed optimally, so that the accelerated roll is prevented from carrying out unnecessary revolutions until the gluing, or the roll is prevented from reaching the web speed too late and the old roll is prevented from being used up before the gluing is carried out.Consequently, faulty gluing with the occurrence of printer's waste and machine standstill time are avoided.

The control means also makes it possible to determine the moment of inertia of the replacement roll at the beginning of the acceleration process. By this means, the braking moment can be controlled in dependence on the moment of inertia in the case of braking to a stop during the running-up. If the roll is of a small size, the adhesive tip in the case of peripheral drive and the spool sleeve in the case of central drive are preserved and the risk of faulty gluing, machine standstill, lowered printing speed or shunting-out of rolls is reduced. The roll mass can also be determined in simple manner from the moment of inertia and is available for, for example, the process data acquisition of the processing machine.

Finally, the acceleration of all replacement rolls by the same tangential acceleration entails the advantage that the adhesive tip, even in the case of small rolls, is not exposed to increased inertia force and thereby to the risk of the lifting-off.

Embodiments of the present invention will now be more particularly described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a schematic block diagram of first control means, with belt drive, embodying the invention; and Fig. 2 is a schematic block diagram of second control means, with central drive, embodying the invention.

Referring now to the drawings there is shown roll drive control means which, in the embodiment of Fig. 1 co-operates with a doublearmed roll stand 1, which carries an old roll 2 and a replacement roll 3. A material web 4 is unwound from the old roll 2 and fed to a processing machine (not shown), for example a printing machine. The web in that case drives a web-guiding roller 5 with a web pulse transmitter 6, which is connected to a computer and storage unit 7. Each arm of the roll stand 1 carries a revolution pulse transmitter 8 or 9, which for each revolution of the roll delivers a pulse. By means of a changeover switching device 10, the revolution pulse transmitter 8 associated with the replacement roll is connected with the unit 7. A drive belt 11, which is drivably coupled to a direct current motor 12, bears against the replacement roll 3.In addition, a tachogenerator 13 and a circumferential pulse transmitter 14 are connected with the direct current motor 12. Whilst the circumferential pulse transmitter 14 is connected to the computer and storage unit 7, the tachogenerator 13 feeds a differentiating member 15, which is connected at its output with an actual value input of a comparison member 16. A target value input of the comparison member 16 is connected with the unit 7 and the output of the member with a regulating device 17. Connected behind the latter is a rotational speed controller 18, the output of which is connected to a control member of the motor 12. A current transformer 19, which with the interposition of a current-voltage converter 20 is connected to the-unit 7, lies in the armature current circuit of the motor 12. The unit 7 is also connected with the regulating device 17.

In the following description, the formula symbols have the significance set out below: at tangential acceleration atBr tangential retardation D diameter of the replacement roll f function 1M armature current of the accelerating motor moment of inertia of the central drive JG moment of inertia of the belt drive JK moment of inertia of the roll bearing (cone) JR moment of inertia of the replacement roll K1 to K g constants MAG driving torque in the case of belt drive MAZ driving torque in the case of central drive MBrG braking torque for belt braking MBrZ braking torque for central braking MR friction torque of the roller bearing MRG friction torque of the belt drive m mass of the replacement roll N circumferential path per circumferential pulse n rotational speed of the accelerating motor S web path per web pulse Tv time interval ta acceleration time web speed VU circumferential speed ZB number of web pulses ZD number of revolution pulses ZU number of circumferential pulses angular speed of the accelerating motor In the course of a roll change operation, which is not described in more detail, the replacement roll 3 is to be glued to the material web 4 of the old roll 2 as it comes to an end. For this purpose, the replacement roll 3 is accelerated by means of the motor 12 in its circumferential speed VU from zero to the material web speed VB.

This takes place at constant tangential acceleration at, which is preset, in the present embodiment, by a voltage at the comparison member 16. This target value is put into storage in the computer and storage unit 7. A different target value transmitter, for example a potentiometer, can also be used, this being connected with the computer and storage unit 7 and the comparison member 16. The actual value of the tangential acceleration is obtained as a voltage value through differentiation of the voltage of the tachogenerator 13 against time in the differentiating member 15 and fed to the comparison member 16. From the target value deviation determined therein, a control magnitude is derived in the regulating device 17. The rotational speed controller 18 acted on thereby brings about a corresponding change in the rotational speed of the direct current motor 12.

By reason of the linear relationship of the increase in circumferential speed per unit of time in the case of constant tangential acceleration, the required acceleration time ta of the replacement roll 3 results from the relationship Vg ta = (1) at or ta = K1.vB (2) with K1 = 1 (3) at as constant The web speed vg is determined in the computer and storage unit 7 from the number of web pulses ZB of the web pulse transmitter 6 over a preset time interval Tv and the web path S per web pulse according to the equation ZB.S (4) vB = Tv For the driving torque MAG of the accelerating motor in the case of belt drive, there applies 4JR.at + 4JK . at + 2MR MAG = MRG + JG.at.K2 + D2#K2 D2#K2 D.K2 (5) with K2 = # = 2r (6) vU vU From equation (5), the moment of inertia JR of the replacement spool roll 3 results as MAG.D2.K2 MRG.D2.K2 3 3G.DZ .KI - JK MR.D (7) JR = 4at 4at 4 2at In that case, the driving torque MAG is a known function of the armature current 1M of the direct current motor 12 MAG = f (IM) (8) The value of the armature current 1M is supplied by the current transformer 19 and, converted by means of the current-voltage converter 20 into a voltage, fed to the computer and storage unit 7.

By equation (8) and the constants K3 = K2 (9) 4 K = MRG.K2 (10) 4 K5 = H (11) 4 K6 = 2R (12) K7 = JK (13) Eauation (7) can be converted into

The constants are fixed specifically to the unwinding the function of the armature current is equally fixed and the tangential acceleration at is preset. The initial diameter D of the replacement roll 3 is determined in the computer and storage unit 7 during its first rotation from the number of circumferential pulses ZU of the circumferential pulse transmitter 15 between two pulses ZD of the rotation pulse transmitter 18 and the circumferential path N per circumferential pulse according to the equation ZU.N (15) D r: Thus, the moment of inertia JR can now be calculated by the computer and storage unit 7.

At the same instant, the mass m of the replacement spool roll is calculable by 8 JR m= (16) and can,for example, be used for process data of the processing machine.

By the availability of the moment of inertia JR, analogously to the components acting during acceleration, the braking moment MBrG for belt braking of the replacement roll is calculable by MBrG = - MRG + JG.atgr.K2 + 4 JR.atBr 4 JK.atBr 2 MR D2.K2 + - l-------.K2 (17) wherein the tangential retardation atBr is present. In the case of braking to a stop, the braking torque MBrG calculated by the computer and storage unit 7, is fed in the form of a voltage to the regulating device 17. The latter thereupon discontinues the acceleration regulation of the replacement roll 3 and drives the controller 18 in such a manner that the motor 12 operating in four-quadrant operation produces the braking torque.

In the embodiment of Fig. 1, the acceleration of the replacement roll takes place by means of a motor. The drive of the replacement roll can also take place from the main drive of the processing machine, for example by way of an electrical coupling acting as control member, Then, the corresponding dependence of the torque transmitted by the coupling on the exciting current and the constant K5 changed in the moment of inertia JG by the component of the coupling is to be put into the computer and storage unit.

Illustrated in Fig. 2 is apparatus which contains a double-armed roll stand 21. The latter carries the old roll 22 and the replacement roll 23. A material web 24 is unwound from the old roll 22 and conducted by way of a web-guiding roller 25, which carries a web pulse transmitter 27 connected to a computer and storage unit 26. A direct current motor 29 drives a spindle 28 of the replacement roll 23 and a direct current motor 31 drives a spindle 30 of the old roll 22. Each arm of the roll stand 21 carries a revolution pulse transmitter 32 and 33, which supplies one pulse per revolution of the respective roll. The direct current motor and revolution pulse transmitter associated with the replacement roll become effective by means of change-over switching devices 34 and 35.In that case, in Fig. 2, the transmitter 32 is connected with the unit 26 and the motor 29 with the output of a controller 36.

Bearing against the shell of the replacement roll 23 is a roller 37, with which are coupled a circumferential pulse transmitter 38 connected to the unit 26 and a tachogenerator 39. The latter feeds a differentiating member 40. Its output is conducted to an actual value input of a comparison member 41, a target value input of which is connected with the unit 26 and the output of which is connected with a regulating device 42. The output of the latter is connected to the controller 36. Arranged in the armature current path for the motors 29 and 31 is a current transformer 43 which, subject to interposition of a current-voltage converter 44, is connected with the unit 26. The latter is also connected with the regulating device 42.

In the course of the roll change operation, the replacement roll 23 is glued to the web 24 of the old roll 22 approaching its end. For this purpose, the replacement roll 23 is accelerated in its circumferential speed vU from zero to the web speed vB by means of the motor 29. This takes place at a constant tangential acceleration at, which in the Fig. 2 embodiment is represented by a voltage preset at the comparison member 41. The unit 26, into which the target value of the tangential acceleration at has been entered, functions as a target value transmitter. The actual value of the tangential acceleration is obtained as a voltage value through differentiation of the voltage of the tachogenerator 39 against time in the differentiating member 40 and fed to the comparison member 41.By means of the target value deviation determined therein, a control magnitude is derived in the regulating device 42. The controller 36 acted on thereby brings about a corresponding change in the rotational speed of the motor 29.

For the determination of the acceleration time ta of the replacement spool roll 23, analogously to the first embodiment, the equation (2) applies ta = K1-VB (2) with K1 = 1 (3) at as constant.

Analogously, also the web speed vg according to equation (4) VB = - (4) Tv is determined from the number of web pulses ZB of the web pulse transmitter 27 over a preset time interval Tv and the web travel S per web pulse.

For the driving torque MAZ of the accelerating motor in the case of central drive, there applies MAZ = 2 JR.at + 2 JZ + JK.at + MR. (18) D D The moment of inertia JR of the replacement roll 23 results from equation (19) as JR = MAZ.D - JZ - JK - MR.D . (19) 2 at 2at In that case, the driving torque MAZ is a known function of the armature current 1M of the direct current motor 29 MAZ = f (IM)- (20) The value of the armature current 1M is supplied by the current transformer 43 and, converted by means of the current-voltage converter 44 into a voltage, fed to the computer and storage unit 26.

By equation (20) and the constants MR K8 = (21) 2 Kg = Jz + JK (22) equation (19) can be converted into

The constants K8 and Kg are fixed specifically for the unwinding, the function of the armature current is equally fixed and the tangential acceleration at is preset. The initial diameter D of the replacement roll 23 is determined, as for the accelerating device with belt drive during the first roll revolution according to equation (15) ZU.N D = (15) Ir from the number of circumferential pulses ZU of the circumferential pulse transmitter 28 between two pulses ZD of the revolution pulse transmitter 32 and the circumferential travel N per circumferential pulse in the computer and storage unit 26. Thus, by means of the latter, the moment of inertia JR can now be calculated according to equation (23).

At the same instant, the mass m of the replacement roll 23 is calculable according to equation (16) 8 JR .

m = D2 (16) With the availability of the moment of inertia JR, analagously to the components acting during the acceleration, the braking torque MBrZ for central braking of the replacement spool roll 23 is calculable by MBrZ = 2 JR.atgr 2(Jz + '3).at - MR , (24) 0 D wherein the tangential retardation atBr is preset. In the case of braking to a stop, the braking torque MBrZ calculated by the unit 26 is fed in the form of a voltage to the regulating device 42. The latter thereupon discontinues the acceleration regulation of the replacement roll 23 and drives the controller 36 in such a manner that the motor 29 operating in four-quadrant operation produces the braking torque.

In the illustrated embodiments, the roll stands each carry two arms, but the stands could equally well be three-armed.

Moreover, the computer and storage unit can also be fed by analog measurement value transmitters. The measurement value transmitter for the rotational speed of the replacement roll can also deliver one pulse sequence per revolution, wherein the ratio of the pulses per revolution and the evaluated pulses is included as a factor into formula (15).

Equally, a digital transmitter is usable for the driving of the differentiating member, if required with the interposition of a digital-to-analog converter. The differentiating member and the computer and storage unit can also be connected to a common measurement value transmitter for the circumferential speed of the replacement roll.

Claims (3)

1. Control means for controlling roll drive in apparatus for unwinding rolls of web material, the control means comprising drive means for a replacement roll of web material, a speed controller to provide a control value for controlling the driving speed of the drive means, regulating means to regulate the speed controller, actual value determing means to determine the actual values of rotational speed of the replacement roll, circumferential speed of the replacement roll and speed of movement of web material withdrawn from a further roll being unwound, storage and processing means for storing and processing the determined actual values and the control value, target value determining means to determine a target value for tangential acceleration of the replacement roll, the target value determining means being connected to the storage and processing means, differentiating means to differentiate the actual value of circumferential speed of the replacement roll for determining the actual value of tangential acceleration of the replacement roll, and comparison means to compare the actual and target values of tangential acceleration and to control the regulating means in dependence on the comparison result.

2. Control means substantially as hereinbefore described with reference to Fig. 1 of the accompanying drawings.

3. Control means substantially as hereinbefore described with reference to Fig. 2 of the accompanying drawings.