REDUCING TENSILE FORCE-INDUCED CHANGES IN THICKNESS DURING ROLLING

Abstract

A position controller that controls an actuator that sets a roll gap of a roll stand by determining an actuating variable (q) for the actuator as a function of a resulting position target value (s*) and a position actual value(s) of the actuator. The (s*) is determined with a resulting base target value (s1*), which is determined as the sum of an initial base target value (s0*) and an additional target value (δs1*), which is determined by a determination element with an inlet-end actual tension (ZE) and an inlet-end reference tension (ZER) and/or with an outlet-end actual tension (ZA) and an outlet-end reference tension (ZAR). Instead of (ZE) and (ZA), the corresponding target tensions (ZE*, ZA*) of corresponding tension control operations can also be used. However, in both cases, (ZER) and (ZAR) are variables that differ from (ZE*) and (ZA*).

Description

FIELD OF THE INVENTION

The present invention is based on an operating method for a roll stand for rolling flat metal rolling stock,

• • wherein a position regulator for regulating the positioning of an actuator by means of which a roll gap of the roll stand is set determines an actuating variable for the actuator as a function of a resulting position target value and a position actual value of the actuator and activates the actuator accordingly,
  • wherein the resulting position target value is determined by use of a resulting base target value,
  • wherein the resulting base target value is determined as the sum of an initial base target value and an additional target value.

In the simplest case, the resulting position target value is identical to the resulting base target value. The initial base target value is generally independent of the inlet-side tension and the outlet-side tension.

The present invention is furthermore based on a control system for a roll stand for rolling flat metal rolling stock, wherein the control system is formed by hardware blocks and/or software programs in such a way that during operation it implements such an operating method.

The present invention is furthermore based on a rolling unit for rolling flat metal rolling stock, wherein the rolling unit has a roll stand for rolling the flat rolling stock and such a control system.

PRIOR ART

When rolling flat metal rolling stock, one of the fundamental requirements of the rolling process consists in producing flat rolling stock with a thickness that matches a predetermined target thickness as well as possible. The thickness of the rolling stock exiting the roll stand is set in particular via the roll gap. The size of the roll gap is in turn set by corresponding setting of the actuator to a certain position.

The size of the roll gap and hence the thickness of the exiting rolling stock is, however, not fixed solely by the position of the actuator. Instead, the deflection of the roll stand has to be taken into account in addition to wear, thermal crowning, displacement of the rolls, and possibly also other influences. The deflection is a result of the rolling force and further forces acting on the roll stand, for example the bending force.

In most cases, roll stands are operated by regulating the roll gap. In such cases, an outlet-side thickness to which the rolling stock is to be rolled in the roll stand is first determined in a pass schedule. An associated expected rolling force is furthermore determined taking into account parameters of the rolling stock (for example, its width, its inlet-side thickness, its temperature, and other variables). The associated deflection of the roll stand is determined by the use of a spring model of the roll stand. A position target value for the actuator is then determined taking into account the deflection of the roll stand and other variables such as, for example, wear-induced, and/or temperature-induced crowning.

When rolling the rolling stock, the actual rolling force is measured directly or is determined on the basis of measured variables. The correction value is determined by means of an AGC (automatic gauge control). The correction value is determined within the AGC via a spring model of the roll stand.

Flat metal rolling stock is often rolled in such a way that, whilst it is being rolled in the roll stand, the rolling stock is tensioned upstream from the roll stand in an upstream device and/or is tensioned downstream from the roll stand in a downstream device. As a result, an inlet-side tension can be applied to the rolling stock upstream from the roll stand and an outlet-side tension can be applied to it downstream from the roll stand. In order to better maintain the inlet-side and outlet-side tension, a respective loop lifter can be arranged upstream and/or downstream from the roll stand. If the roll stand is a constituent part of a multi-stand rolling line but is not the front roll stand of the rolling line, the upstream device can furthermore be a further roll stand of the multi-stand rolling line. Similarly, if the roll stand is a constituent part of a multi-stand rolling line but is not the last roll stand of the rolling line, the downstream device can also be a further roll stand of the multi-stand rolling line. In other designs, the upstream and/or downstream device can also be a coiler, for example in the case of a Steckel mill. Other embodiments are also possible.

The outlet-side tension and, to an even greater extent, the inlet-side tension have an influence on the rolling force. In particular, the required rolling force is lower, the greater the tensions. The roll stand deflects less in the case of a lower rolling force. If the reduced deflection is not taken into account, the tensions therefore influence the thickness to which the rolling stock is rolled in the roll stand.

In principle, this does not represent a problem because the change in the rolling force is measured and the change in the deflection, effected by the change in the rolling force, is corrected via the already mentioned AGC. However, the AGC needs a significant period of time to correct the deflection of the roll stand. The correction value is thus applied only with a delay. Furthermore, the compensation by the AGC is often taken into account only in an attenuated fashion because otherwise there is a risk that simultaneously correcting the positioning by the AGC and updating the tensions by tension regulating systems can cause oscillations and instabilities. Lastly, the correction value determined by the AGC is often subject to error, for example because of friction effects in the roll stand or because of deadbands.

It is furthermore common practise to switch on the AGC only after the initial pass, i.e. with a delay. During the initial pass, the outlet-side tension is 0 because the head of the rolling stock has not yet reached a downstream device which could apply the outlet-side tension to the rolling stock in conjunction with the roll stand. It is, however, entirely possible that the inlet-side tension has values other than 0. If in such a case the inlet-side tension changes, this has effects on the rolling force and hence on the deflection of the roll stand. However, because the AGC is switched on only after the initial pass, the change in the thickness, caused by the changed deflection of the roll stand, to which the rolling stock is rolled in the roll stand is not corrected during the initial pass.

Similarly, it is common practise to freeze the AGC already before the final pass, i.e. in advance, (in other words, to no longer update a correction value determined at the time of the freezing) or to limit the time for which the correction value is changed. During the final pass, the inlet-side tension is 0 because the tail of the rolling stock has already exited an upstream device which could apply the inlet-side tension to the rolling stock in conjunction with the roll stand. It is, however, entirely possible that the outlet-side tension has values other than 0. If in such a case the outlet-side tension changes, this has effects on the rolling force and hence on the deflection of the roll stand. However, because the AGC is already frozen before the final pass and the time for which the correction value determined by the AGC is changed is limited, the change in the thickness, caused by the changed deflection of the roll stand, to which the rolling stock is rolled in the roll stand is not corrected, or only insufficiently, during the final pass phase.

EP 3 231 522 A1 discloses an operating method of the type mentioned at the beginning. In this operating method, a positioning additional target value which is added to the actual positioning target value is determined by means of a tension regulator which regulates the input-side actual tension to an input-side target tension. The actual positioning target value is a roll gap target value.

JP 2003-164 906 A also discloses an operating method of the type mentioned at the beginning. In this operating method, a positioning additional target value which is added to the actual positioning target value is determined by means of a tension regulator which regulates the output-side actual tension to an output-side target tension. The actual positioning target value is a roll gap target value.

EP 2 620 233 A1 also discloses an operating method for a roll stand for rolling flat metal rolling stock. In this operating method, a mass flow regulation is implemented which for its part acts on the positioning system of the roll stand. The thickness of the rolling stock exiting the roll stand is set as a result. In this operating method, a tension regulator which regulates the input-side actual tension to an input-side target value acts on the positioning system of the roll stand.

SUMMARY OF THE INVENTION

The object of the present invention consists in providing options by means of which better maintenance of the thickness of the rolling stock at the outlet side of the roll stand can be ensured.

The object is achieved by an operating method having the features of claim 1. Advantageous embodiments of the operating method are the subject of the dependent claims 2 to 12.

According to the invention, an operating method of the type mentioned at the beginning is configured such that

• • the additional target value is determined by a determination element by the use of an inlet-side actual tension, or a corresponding target tension of an inlet-side tension regulating system, and an inlet-side reference tension and/or by the use of an outlet-side actual tension, or a corresponding target tension of an outlet-side tension regulating system, and an outlet-side reference tension,
  • wherein the inlet-side reference tension is a different variable from the inlet-side target tension and/or the outlet-side reference tension is a different variable from an outlet-side target tension.

The inlet-side actual tension and/or the outlet-side actual tension can be actual values measured using measurement technology or be values determined on the basis of values measured using measurement technology. The use of either the actual values or the target values is possible because the tension regulating systems generally have a sufficiently high dynamics and quality and therefore the actual values and the target values coincide to a sufficient extent.

The roll stand is generally operated by regulating the roll gap. Furthermore, the inlet-side tension regulating system generally acts on a roll circumferential speed at which the flat rolling stock is rolled in the roll stand, and/or on a feed speed at which the flat rolling stock exits a device arranged upstream from the roll stand. Similarly, the outlet-side tension regulating system generally acts on the roll circumferential speed and/or on a discharge speed at which the flat rolling stock enters a device arranged downstream from the roll stand. The tension regulating systems generally in each case act on only one device, i.e. either the upstream device or the roll stand, or either the roll stand or the downstream device.

Provided that a dependency of the additional target value on the inlet-side tension state (target or actual) exists, the additional target value is determined by the determination element preferably on the basis of the product of an inlet-side sensitivity and the difference between the inlet-side actual tension or the corresponding target tension and the inlet-side reference tension. Similarly, the additional target value is determined by the determination element preferably on the basis of the product of the outlet-side sensitivity and the difference between the outlet-side actual tension or the corresponding target tension and the outlet-side reference tension, provided that there is a dependency of the additional target value on the outlet-side tension state. Determination of the additional target value and hence the resulting base target value is consequently configured particularly simply.

The additional target value is preferably determined by the determination element on the basis of the product of an inlet-side sensitivity and the difference between the inlet-side actual tension or the corresponding target tension and the inlet-side reference tension and/or on the basis of the product of the outlet-side sensitivity and the difference between the outlet-side actual tension or the corresponding target tension and the outlet-side reference tension. In this way, the additional target value can be determined particularly simply and reliably.

The inlet-side sensitivity and/or the outlet-side sensitivity are preferably specified for the determination element by a higher-order control device.

The corresponding sensitivities can, for example, be saved within the higher-order control device in the form of tables or the like. The corresponding sensitivities can be saved in the tables depending on the geometry and other properties of the rolling stock (for example, its chemical composition and its temperature). It is, however, preferred if the inlet-side sensitivity and/or the outlet-side sensitivity are determined by the higher-order control device as part of a pass schedule calculation by analysis of a rolling model. The rolling model is based on mathematical physical equations which describe the rolling procedure in the roll stand. Very precise determination of the inlet-side sensitivity and/or the outlet-side sensitivity is consequently possible. The rolling model can, if necessary, be adapted again and again.

The mathematical physical equations of the rolling model are generally differential equations and/or algebraic equations. Such models are widely known to a person skilled in the art. Reference can be made purely by way of example to the scientific paper “On the theory of rolling” by J. M. Alexander, published in the Proceedings of the Royal Society of London, Vol. 326, pages 535 to 563 (1972).

Similarly, the inlet-side reference tension and/or the outlet-side reference tension can also be specified for the determination element by a higher-order control device. The corresponding reference tensions can be determined or set by the higher-order control device as part of a pass schedule calculation.

The operating method is preferably configured in such a way that the higher-order control device, for example as part of a pass schedule calculation,

• • determines the initial base target value and the inlet-side target tension and/or the outlet-side target tension on the basis of a target thickness with which the flat rolling stock is to exit the roll stand and the inlet-side reference tension and/or the outlet-side reference tension,
  • specifies the initial base target value of a regulating unit comprising the position regulator and the determination element, and
  • specifies the inlet-side target tension for a front tension regulator which regulates the inlet-side actual tension to the inlet-side target tension, and/or specifies the outlet-side target tension for a rear tension regulator which regulates the outlet-side actual tension to the outlet-side target tension.

The resulting position target value is preferably determined at least during the rolling of a central portion of the rolling stock by the use of a correction value determined by the use of an actual rolling force. An AGC is thus implemented. It is therefore possible to combine the operating method according to the invention with the AGC.

The resulting base target value is preferably taken into account as part of the determination of the correction value in addition to the actual rolling force. The dynamics can be improved as a result when determining the correction value.

The resulting position target value is preferably determined at least during the rolling of a head of the rolling stock and/or a tail of the rolling stock without the use of an actual rolling force. In this case, by means of the present invention, compensation is also made of tension changes and rolling force changes caused thereby when the AGC is not active.

The latter procedure can be combined in particular also with the procedure in which the AGC is active during the rolling of a central portion of the rolling stock. In this case, the AGC can alternatively be switched on at the transition from rolling the head of the rolling stock to rolling the central portion. Similarly, the AGC can be switched off (frozen or its changes limited) at the transition from rolling the central portion to rolling the tail of the rolling stock.

The resulting position target value is preferably determined by the use of the deviation of a thickness of the rolling stock, measured at the outlet side of the roll stand, from a target thickness. Any remaining errors can be corrected as a result.

The object is furthermore achieved by a control system having the features of claim 13. According to the invention, the control system implements an operating method according to the invention during operation using the hardware blocks and/or software programs.

The object is furthermore achieved by a rolling unit having the features of claim 14. According to the invention, the control system is designed as a control system according to the invention in the case of a rolling unit of the type mentioned at the beginning.

SHORT DESCRIPTION OF THE DRAWINGS

The abovedescribed properties, features, and advantages of this invention and the manner in which they are achieved will become clearer and more readily understandable in conjunction with the following description of the exemplary embodiments which are explained in detail in connection with the drawings in which, illustrated schematically:

FIG. 1 shows a roll stand and its control system,

FIG. 2 shows a roll assembly in a first operating state,

FIG. 3 shows the roll assembly from FIG. 2 in a second operating state,

FIG. 4 shows the roll assembly from FIG. 2 in a third operating state,

FIG. 5 shows the structure of a regulating unit,

FIG. 6 shows a determination element,

FIG. 7 shows a supplement to the regulating unit from FIG. 5,

FIG. 8 shows a modification to the supplement from FIG. 7,

FIG. 9 shows a time diagram, and

FIG. 10 shows an embodiment of the regulating unit from FIG. 5.

DESCRIPTION OF THE EMBODIMENTS

In FIG. 1, rolling stock 2 is to be rolled in a roll stand 1. Only the working rollers of the roll stand 1 are illustrated in FIG. 1 (and, where illustrated, also in the other Figures). However, the roll stand 1 generally has at least back-up rollers in addition to the working rollers (four-high stand), possibly also intermediate rollers, which are arranged between the working rollers and the back-up rollers, in addition to the back-up rollers (six-high stand). The rolling stock 2 is made from metal, often from steel, in many cases from aluminum, rarely from another metal such as, for example, copper. The rolling stock 2 is furthermore flat rolling stock, i.e. a strip (the norm) or a heavy plate (the exception).

The roll stand 1 is generally operated by regulating the roll gap. Furthermore, the rolling stock 2 is rolled in the roll stand 1 at a roll circumferential speed vU. The associated drives and their activation are not illustrated.

According to the illustration in FIGS. 2 and 3, the rolling stock 2 can be held in a device 3 upstream from the roll stand 1 whilst it is being rolled in the roll stand 1. In this case, the rolling stock 2 exits the upstream device 3 at a feed speed vZ. Furthermore, an inlet-side actual tension ZE is applied to the rolling stock 2 on the inlet side of the roll stand 1. A loop lifter can be arranged between the upstream device 3 and the roll stand 1. The loop lifter is not illustrated. The upstream device 3 can be designed in accordance with the illustration in FIGS. 2 and 3 in particular as a further roll stand. It can, however, also have a different design, for example as a coiler or as a set of driving rollers. The feed speed vZ is illustrated in FIG. 2 as a circumferential speed. If the upstream device 3 is a roll stand, the forward slip must additionally be taken into account.

The inlet-side actual tension ZE is generally regulated to a corresponding target tension ZE* by means of a corresponding tension regulating system. In this case, the inlet-side actual tension ZE and the inlet-side target tension ZE* are supplied to a front tension regulator 24. The front tension regulator 24 determines, by the use of the inlet-side actual tension ZE and the inlet-side target tension ZE*, usually by the use of the difference between the two said tensions ZE, ZE*, a front actuating variable δvE which is applied to an actuator such that the inlet-side actual tension ZE is aligned to or at least approximated with the inlet-side target tension ZE*. The front actuating variable δvE can in particular be a speed additional target value which acts on the roll circumferential speed vU or, with the sign reversed, acts on the feed speed vZ.

Similarly, the rolling stock 2 can be held, in accordance with the illustration in FIGS. 3 and 4, in a device 4 downstream from the roll stand 1 whilst it is being rolled in the roll stand 1. In this case, the rolling stock 2 enters the downstream device 4 at a discharge speed vA. Furthermore, an outlet-side actual tension ZA is applied to the rolling stock 2 on the outlet side of the roll stand 1. A loop lifter can also be arranged between the roll stand 1 and the downstream device 4. This loop lifter is not illustrated either. The downstream device 4 can be designed in particular as a further roll stand in accordance with the illustration in FIGS. 3 to 5. It can, however, also have a different design, for example as a coiler or as a set of driving rollers. The discharge speed vA is illustrated in FIGS. 3 and 4 as a circumferential speed. If the downstream device 4 is a roll stand, the backward slip must additionally be taken into account.

The outlet-side actual tension ZA is generally regulated to a corresponding target tension ZA* by means of a corresponding tension regulating system. In this case, the outlet-side actual tension ZA and the outlet-side target tension ZA* are supplied to a rear tension regulator 25. The rear tension regulator 25 determines, by the use of the outlet-side actual tension ZA and the outlet-side target tension ZA*, usually by the use of the difference between the two said tensions ZA, ZA*, a rear actuating variable δvA which is applied to an actuator such that the outlet-side actual tension ZA is aligned to or at least approximated with the outlet-side target tension ZA*. The rear actuating variable δvE can in particular be a speed additional target value which acts on the roll circumferential speed vU or, with the sign reversed, acts on the discharge speed vA.

The roll stand 1 generally has a large number of actuators by means of which the rolling process is influenced. Examples of such actuators are a bending system by means of which a roll bend can be set, a displacement device by means of which a pair of rolls can be displaced axially in opposite directions, a roll cooling system, a roll gap lubrication system, and many others. Within the scope of the present invention, it is essentially an actuator 5 (see FIG. 5) by means of which the roll gap of the roll stand 1 is set. More details will therefore be given below only about this actuator 5 and its activation.

In order to regulate the positioning of the actuator 5, a position target value s* is specified for a position regulator 6 of a regulating unit 7. An actual value s of the actuator 5 is furthermore supplied to the position regulator 6. As a function of these two variables s*, s, the position regulator 6 determines an actuating variable q for the actuator 5 and controls the actuator 5 accordingly. The regulating unit 7 is an essential constituent part of a control system according to the invention.

The actuator 5 is generally designed, in accordance with the illustration in FIG. 5, as a hydraulic cylinder unit. In this case, the actuating variable q acts on a hydraulic system 8 by means of which a high working pressure pP (=pump pressure) or a low working pressure pT (=tank pressure) is applied as required to working chambers 9, 10 of the hydraulic cylinder unit. The actuating variable q can in this case be a hydraulic flow to be delivered. In particular in this embodiment, the position regulator 6 can, in accordance with the illustration in FIG. 5, be designed as a proportional regulator (P regulator). In rare cases, alternatively or additionally, adjustment of the roll gap by means of electric drives which act on screws is also possible. In such cases, the position regulator 6 is often designed as a proportional-integral regulator (PI regulator).

The resulting position target value s* is determined by the use of a resulting base target value s1*. In the embodiment according to FIG. 5, the resulting position target value s* is identical to the resulting base target value s1*. Further variables can, however, also be included in the resulting position target value s*. This will become more apparent from further explanations. The resulting base target value s1* is determined by the use of the inlet-side actual tension ZE and/or the outlet-side actual tension ZA.

In accordance with the illustration in FIG. 5, the resulting base target value s1* is determined in a node point 11 as the sum of an initial base target value s0* and an additional target value δs1*. The initial base target value s0* is, at least generally, independent of the inlet-side actual tension ZE and the outlet-side actual tension ZA. The additional target value δs1* is, in contrast, dependent on the inlet-side actual tension ZE and the outlet-side actual tension ZA. In particular, the additional target value δs1* is determined by the determination element 13 by the use of an inlet-side actual tension ZE and an inlet-side reference tension ZER. Alternatively or additionally, the additional target value δs1* can be determined by the determination element 13 by the use of the outlet-side actual tension ZA and an outlet-side reference tension ZAR.

In order to determine the additional target value δs1*, in accordance with the illustration in FIG. 6, the inlet-side actual tension ZE can be supplied, for example, to a determination block 12 of the determination element 13. In this case, an inlet-side component δs1E* of the additional target value δs1* is determined in the determination block 12 by the use of the inlet-side actual tension ZE and the inlet-side reference tension ZER. For example, the inlet-side component δs1E* can be determined, in accordance with the illustration in FIG. 6, according to the formula

δs1E*=SE·(ZE−ZER)  (1)

where SE is an input-side sensitivity. The input-side reference tension ZER can optionally have the value 0. In a particular case, it can even be variable over time. In this case, it is generally also necessary to change the initial base target value to a corresponding extent.

The input-side sensitivity SE and the input-side reference tension ZER can be specified for the determination element 13, for example, in accordance with the illustration in FIG. 1 by a higher-order control device 14. The control device 14 is, where present, a further essential constituent part of the control system.

Similarly, in order to determine the additional target value δs1*, in accordance with the illustration in FIG. 6, the outlet-side actual tension ZA is supplied, for example, to a determination block 15 of the determination element 13. In this case, an outlet-side component δs1A* of the additional target value δs1* is determined in the determination block 15 by the use of the outlet-side actual tension ZA and the outlet-side reference tension ZAR. For example, the outlet-side component δs1A* can be determined in accordance with the illustration in FIG. 6, according to the formula

δs1A*=SA·(ZA−ZAR)  (2)

where SA is an output-side sensitivity. The outlet-side sensitivity SA and the outlet-side reference tension ZAR can likewise be specified for the determination element 13 by the higher-order control device 14 in accordance with the illustration in FIG. 1. The input-side reference tension ZAR can optionally have the value 0. In a particular case, it can even be variable over time. In a similar way to changing the inlet-side reference tension ZER, at one end of the outlet-side reference tension ZAR it may be necessary to change the initial base target value s0* to a corresponding extent.

It is possible that only one of the two tensions ZE, ZA is used. In this case, the additional target value δs1* is identical to the corresponding component δs1E*, δs1A*. However, generally both tensions ZE, ZA are used. In the case of a linearized determination, the determination element 13 has a node point 16 in which the additional target value δs1* is determined as the sum of the two components δs1E*, δs1A*. It is furthermore possible to use the associated target values ZE*, ZA* instead of the actual values ZE, ZA.

The target tensions ZE*, ZA*, i.e. the target values ZE*, ZA* supplied to the associated tension regulators 24, 25 and hence valid for the tension regulating systems, are different variables from the reference tensions ZER, ZAR. Although in this approach it can be possible to derive the target tensions ZE*, ZA* from the reference tensions ZER, ZAR, there is, however, no identity between them. Although the specific values can temporarily be the same, this is, however, not systematic and not always the case.

It is thus, for example, possible that the target tensions ZE*, ZA* are specified by an operator (not illustrated) or can be varied by the operator during the rolling of the flat rolling stock 2. In contrast, the reference tensions ZER, ZAR cannot be changed by the operator. It is furthermore possible that the target tensions ZE*, ZA* are varied over time by the higher-order control device 14 for technological reasons, whilst the reference tensions ZER, ZAR are maintained. This will be explained in detail below with the aid of an example. In this example it is assumed that the upstream device 3 and the downstream device 4 are roll stands and furthermore a roll stand is also arranged upstream from the upstream device 3, and a roll stand is also arranged downstream from the downstream device 4.

The head 20 of the rolling stock 2 (see FIG. 2) reaches the roll stand 1 at a point in time t1, the downstream device 4 at a point in time t2, and the roll stand arranged downstream from the downstream device 4 at a point in time t3. Similarly, for example, a tail 21 of the rolling stock 2 (see FIG. 4) reaches, for example, the roll stand arranged upstream from the upstream device 3 at a point in time t4, the upstream device 3 at a point in time t5, and the roll stand 1 at a point in time t6. The point in time t4 is generally after the point in time t3.

FIG. 2 shows the rolling process at the point in time t1 when the rolling stock 2 is being rolled. The inlet-side actual tension ZE can be applied after the point in time t1. In contrast, this is not possible before the point in time t1. The inlet-side actual tension ZE is thus necessarily 0 before the point in time t1. The outlet-side actual tension ZA is likewise 0 because no rolling stock 2 is yet situated on the outlet side of the roll stand 1 and in particular the rolling stock 2 has not reached the downstream device 4.

Similarly, FIG. 4 shows the rolling process at the point in time t6 when the rolling stock 2 is being rolled. Up until the point in time t6, the outlet-side actual tension ZA can still be applied but after the point in time t6 this is not possible. The actual tension ZA is thus necessarily 0 after the point in time t6. The inlet-side actual tension ZE is also 0 because there is no longer any rolling stock 2 situated at the inlet side of the roll stand 1 and in particular it has exited the upstream device 3 a long time beforehand.

FIG. 3 shows the rolling process when the rolling stock 2 is being rolled between the points in time t1 and t6, to be more precise between the points in time t2 and t5. The respective actual tension ZE, ZA is applied during this period of time to the rolling stock 2 on at least one side (i.e. on the inlet side or on the outlet side), or even on both sides (i.e. on the inlet side and on the outlet side) during part of this period of time.

In the static state when the rolling stock 2 is being rolled in all the roll stands of the abovementioned example, the target tensions ZE*, ZA* can correspond to the reference tensions ZER, ZAR, i.e. have the same values. This static state, relative to the specification of the target values ZE*, ZA* for the tension regulators 24, 25, exists between the points in time t3 and t4.

In contrast, the rear tension regulator 25 can, for example, in principle be inactive in the period of time between the point in time t1 and the point in time t2. This is because the outlet-side actual tension ZA cannot be applied to the rolling stock 2 at the outlet side of the roll stand 1. In contrast, it is absolutely possible to determine the outlet-side component δs1A* of the additional target value δs1* during this period of time too. Furthermore, although the front tension regulator 24 can be active during this period of time, it is, however, possible that the corresponding target value ZE*=ZER is not supplied immediately to the front tension regulator 24 at the point in time t1 (or shortly thereafter) and instead the target value ZE* is raised by means of a ramp from 0 to the value of the corresponding reference tension ZER.

It is similarly possible that, although the rear tension regulator 25 is active in the period of time between the point in time t2 and the point in time t3, the corresponding target value ZA*=ZAR is not supplied immediately to the rear tension regulator 25 at the point in time t2 (or shortly thereafter) and instead the target value ZA* is raised by means of a ramp from 0 to the value of the corresponding reference tension ZAR.

It is similarly possible that, although the front tension regulator 24 is active in the period of time between the point in time t4 and the point in time t5, the target value ZE* supplied to the front tension regulator 24 is, however, lowered by means of a ramp to the value 0 during the said period of time from the value ZE*=ZER present at the beginning of the said period of time.

Furthermore, the front tension regulator 24 can in principle be inactive in the period of time between the point in time t5 and the point in time t6. This is because the inlet-side actual tension ZE cannot be applied to the rolling stock 2 at the inlet side of the roll stand 1. In contrast, it is absolutely possible to determine the inlet-side component δs1E* of the additional target value δs1* during this period of time too. Furthermore, although the rear tension regulator 25 can be active during this period of time, it is, however, possible that the target value ZA* supplied to the rear tension regulator 25 is lowered during the said period of time by means of a ramp to the value 0 from the value ZA*=ZAR present at the beginning of the said period of time.

The inlet-side sensitivity SE and/or the outlet-side sensitivity SA and possibly also further values such as the reference tensions ZER and/or ZAR and/or the initial base target value s0* can be provided by the higher-order control device 14.

The regulators carry out real-time regulation during the rolling of the rolling stock. The regulators as a whole are usually referred to as an L1 system by experts. The higher-order control device 14 thus functions as a unit which is usually referred to as an L2 system by experts. In accordance with the illustration in FIG. 1, the higher-order control device 14 comprises, inter alia, a rolling model 17 in which the rolling procedure in the roll stand 1 is modeled. The rolling model 17 is based on mathematical physical equations which describe the rolling procedure. The higher-order control device 14 determines the said variables SE and/or SA and/or ZER and/or ZAR and/or s0* and possibly also further variables by analyzing the rolling model 17.

For example, the higher-order control device 14 performs a pass schedule calculation, in which these and if necessary other values are determined, before the rolling stock 2 is rolled in the roll stand 1. The determined values are made available by the higher-order control device 14 to lower-order regulators (for example, to the position regulator 6 of the regulating unit 7). In particular, as part of the pass schedule calculation, the higher-order control device 14 determines the initial base target value s0* and the inlet-side target tension ZE* and/or the outlet-side target tension ZA* on the basis of a target thickness d* (see FIG. 1) with which the flat rolling stock 2 is to exit the roll stand 1, and the inlet-side reference tension ZER and/or the outlet-side reference tension ZAR. The target thickness d* can alternatively be specified for the higher-order control device 14 or be determined independently by the higher-order control device 14. The reference tensions ZER, ZAR are generally set by the higher-order control device 14. Based on these values d*, ZER, ZAR, the higher-order control device 14 determines the required rolling force and the required positioning. The required rolling force corresponds to a reference rolling force FR, and the required positioning to the initial base target value s0*. The initial base target value s0* is specified by the higher-order control device 14 of the regulating unit 7. Also, the higher-order control device 14 specifies the inlet-side target tension ZE* for the front tension regulator 24, and the outlet-side target tension ZA* for the rear tension regulator 25.

The higher-order control device 14 can determine the inlet-side sensitivity SE, for example, by it determining, for the intended working point of the roll stand 1, the effect of the change in the inlet-side tension ZE on an actual rolling force F and furthermore the effect of the change in the rolling force F on the deflection of the roll stand 1. The product of the two said effects gives the inlet-side sensitivity SE. Similarly, the higher-order control device 14 can determine the outlet-side sensitivity SA by it determining, for the intended working point of the roll stand 1, the effect of the change in the outlet-side tension ZA on the rolling force F and furthermore the effect of the change in the rolling force F on the deflection of the roll stand 1. The product of the two said effects gives the outlet-side sensitivity SA. In a completely equivalent fashion, it is also possible to specify the base variables for the sensitivities SE, SA for the determination element 13, i.e. the effect of the change in the inlet-side tension ZE on the actual rolling force F, the effect of the change in the outlet-side tension ZA on the rolling force F, and the effect of the change in the rolling force F on the deflection of the roll stand 1. In this case, the determination element 13 can determine the sensitivities SE, SA itself. Furthermore, the determination element 13 is in this case in particular also capable of determining a change 5F in the expected rolling force corresponding to changes in the tensions ZE, ZA.

The resulting position target value s* is generally not identical to the resulting base target value s1* and instead is determined by the use of further correction variables.

Thus, in accordance with the illustration in FIG. 7, it is, for example, possible that the resulting position target value s* is determined by the use of a correction value δs2* determined by the use of the rolling force F. For example, the resulting position target value s* can be determined in a node point 18 as the sum of the resulting base target value s1* and a correction value δs2*. The correction value δs2* is in this case determined in a determination block 19 by the use of the actual rolling force F. The determination block 19 thus implements an AGC in which an additional deflection of the roll stand 1 is (at least largely) compensated. The additional deflection of the roll stand 1 is caused by the deviation of the actual rolling force F from the reference rolling force FR. For the sake of good order, it should be pointed out that only the additional parts of the regulating unit 7 are illustrated in FIG. 7. FIGS. 5 and 6 should be consulted for the fundamental design of the regulating unit 7.

In the simplest case, only the actual rolling force F and the reference rolling force FR are supplied to the determination block 19 as input variables. In accordance with the illustration in FIG. 1, the reference rolling force FR is provided by the higher-order control device 14. In many cases, however, in addition to the actual rolling force F, a value is also supplied to the determination block 19 which, apart from the correction value δs2* determined by the determination block 19, already corresponds to the resulting position target value s*. For example, the resulting base target value s1* can be supplied to the determination block 19. In this case, as part of the determination of the correction value δs2* the determination block 19 additionally also takes into account the resulting base target value s1*. Furthermore, in this case the determination element 13 also determines the associated expected change 5F in the reference rolling force FR in addition to the additional target value δs1*. The expected change 5F in the reference rolling force FR is taken into account by the determination block 19 when the correction value δs2* is determined. In addition, the position actual value s may also be supplied to the determination block 19.

It is possible that the procedure explained in connection with FIG. 7 is carried out continuously during the rolling of the rolling stock 2 in the roll stand 1. As part of this, the correction value δs2* is determined and updated independently of what portion of the rolling stock 2 is being rolled. In many cases, the correction value δs2* is, however, determined and applied whilst a central portion of the rolling stock 2 is being rolled. In contrast, during the rolling of the head 20 and/or tail 21 of the rolling stock, the resulting position target value s* is often determined by the use of the actual rolling force F. This is explained in detail below in connection with FIGS. 8 and 9 with additional reference to FIGS. 2 to 4.

FIG. 8 is based on the regulating unit 7 from FIG. 7. In FIG. 8, an activation signal A and a reset signal R can be supplied to the determination block 19. The activation signal A has the value 0 or the value 1 in FIG. 9. A value of the activation signal A of 1 causes activation of the determination block 19. In this case, the determination block 19 determines the respective valid correction value δs2* by the use of the rolling force F. As a result, the resulting position target value s* is consequently determined by the use of the rolling force F. A value of the activation signal A of 0 causes deactivation of the determination block 19. In this case, the determination block 19 outputs the last determined correction value δs2* but does not update the correction value δs2* further. As a result, the resulting position target value s* is consequently determined without the use of the rolling force F. The reset signal R is supplied to the determination block 19 only when no rolling stock is being rolled in the roll stand 1. Supplying the reset signal R causes the last determined correction value δs2* to be reset to 0.

The activation signal A varies as a function of time t. Up to the point in time t1, the activation signal A has the zero 0. The activation signal A then increases, generally abruptly, to the value 1. At the point in time t6, the activation signal A falls, again generally abruptly, to the value 0. At a point in time t7, after the point in time t6 in FIG. 9, the reset signal R is specified (for a short period of time).

FIG. 10 shows a further embodiment of the regulating unit 7 from FIG. 5. The embodiment from FIG. 10 could, however, also be readily based on the embodiment of the regulating unit 7 in FIGS. 7 and 8. In FIG. 10, a thickness d of the rolling stock 2, i.e. its actual value, is measured at the outlet side of the roll stand 2 by means of a corresponding measurement device 22. The thickness d is compared with a target thickness d* in a determination block 23. A correction variable δs3* is determined in the determination block 23 on the basis of the deviation of the thickness d of the rolling stock 2 from the target thickness d*. The correction variable δs3* is supplied to the node point 18. The resulting position target value s* is consequently also determined by the use of the correction variable δs3*. All types of remaining errors can be compensated by this procedure.

The present invention has many advantages. If and for as long as the AGC is active, i.e. in particular when rolling the central portion of the rolling stock 2, the AGC and also any thickness regulating system based on the measurement of the thickness d no longer have to compensate all the errors in the positioning of the roll stand 1 caused by the change in the rolling force F because partial compensation is effected anyway by the tension-dependent determination of the resulting position target value s*, i.e. by the correction because of the tensions ZE, ZA. If and for as long as the AGC is inactive, i.e. in particular during the initial pass phase and during the final pass phase, correction of thickness errors can be achieved at least partially by the tension-dependent determination of the resulting position target value s*, which otherwise could not be corrected at all. As a result, the initial portion and/or the end portion of the rolling stock 2, the thickness d of which deviates by more than the permissible tolerance from the target thickness d*, can consequently be shortened considerably, often by approximately half. There is furthermore good reason to believe that the structure of the loop regulating system immediately after the initial pass is also improved.

Although the invention has been illustrated and described in detail by the preferred exemplary embodiment, the invention is not limited to the disclosed examples and other variants can be derived by a person skilled in the art without going beyond the protective scope of the invention.

LIST OF REFERENCE SIGNS

• • 1 roll stand
  • 2 rolling stock
  • 3, 4 up-/downstream device
  • 5 actuator
  • 6 position regulator
  • 7 regulating unit
  • 8 hydraulic system
  • 9, 10 working chambers
  • 11, 16, 18 node points
  • 12, 15, 19, 23 determination blocks
  • 13 determination element
  • 14 control device
  • 17 rolling model
  • 20 head of the rolling stock
  • 21 tail of the rolling stock
  • 22 measurement device
  • 24, 25 tension regulator
  • A activation signal
  • d, d* thicknesses (actual and target)
  • F actual rolling force
  • FR reference rolling force
  • pP, pT working pressures
  • q actuating variable
  • R reset signal
  • s position actual value
  • s* resulting position target value
  • s0*, s1* base target values
  • t time
  • t1 to t7 points in time
  • vA, vU, vZ speeds
  • ZA, ZE, ZA*, ZE* tensions (actual and target)
  • ZAR, ZER reference tensions
  • δs1* additional target value
  • δs1A*, δs1E* components
  • δs2* correction value
  • δs3* correction variable
  • δvA, δvE actuating variables

Claims

1. An operating method for a roll stand for rolling flat metal rolling stock,

determining with a position regulator that regulates positioning of an actuator that sets a roll gap of the roll stand, an actuating variable (q) for the actuator as a function of a resulting position target value (s*) and a position actual value (s) of the actuator; and activating, with the position regulator, the actuator accordingly,

wherein the resulting position target value (s*) is determined by use of a resulting base target value (s1*),

wherein the resulting base target value (s1*) is determined as the sum of an initial base target value (s0*) and an additional target value (δs1*),

wherein the additional target value (δs1*) is determined by a determination element by the use of an inlet-side actual tension (ZE), or a corresponding target tension (ZE*) of an inlet-side tension regulating system, and an inlet-side reference tension (ZER) and/or by the use of an outlet-side actual tension (ZA), or a corresponding target tension (ZA*) of an outlet-side tension regulating system, and an outlet-side reference tension (ZAR), and

wherein the inlet-side reference tension (ZER) is a different variable from the inlet-side target tension (ZE*) and/or the outlet-side reference tension (ZAR) is a different variable from an outlet-side target tension (ZA*).

2. The operating method as claimed in claim 1, wherein the roll stand is operated by regulating the roll gap.

3. The operating method as claimed in claim 1, wherein the inlet-side tension regulating system acts on a roll circumferential speed (vU) at which the flat rolling stock is rolled in the roll stand, and/or on a feed speed (vZ) at which the flat rolling stock exits a device arranged upstream from the roll stand, and/or in that the outlet-side tension regulating system acts on the roll circumferential speed (vU) and/or on a discharge speed (vA) at which the flat rolling stock enters a device arranged downstream from the roll stand.

4. The operating method as claimed in claim 1, wherein the additional target value (δs1*) is determined by the determination element on the basis of the product of an inlet-side sensitivity (SE) and the difference between the inlet-side actual tension (ZE) or the corresponding target tension (ZE*) and the inlet-side reference tension (ZER) and/or on the basis of the product of the outlet-side sensitivity (SA) and the difference between the outlet-side actual tension (ZA) or the corresponding target tension (ZA*) and the outlet-side reference tension (ZAR).

5. The operating method as claimed in claim 4, wherein the inlet-side sensitivity (SE) and/or the outlet-side sensitivity (SA) are specified for the determination element by a higher-order control device.

6. The operating method as claimed in claim 5, wherein the inlet-side sensitivity (SE) and/or the outlet-side sensitivity (SA) are determined by the higher-order control device as part of a pass schedule calculation by analysis of a rolling model which describes the rolling procedure in the roll stand based on mathematical physical equations.

7. The operating method as claimed in claim 1, wherein the inlet-side reference tension (ZER) and/or the outlet-side reference tension (ZAR) are specified for the determination element by a higher-order control device.

8. The operating method as claimed in claim 7, wherein the higher-order control device

determines the initial base target value (s0*) and the inlet-side target tension (ZE*) and/or the outlet-side target tension (ZA*) on the basis of a target thickness (d*) with which the flat rolling stock is to exit the roll stand and the inlet-side reference tension (ZER) and/or the outlet-side reference tension (ZAR),

specifies the initial base target value (s0*) of a regulating unit comprising the position regulator and the determination element, and

specifies the inlet-side target tension (ZE*) for a front tension regulator which regulates the inlet-side actual tension (ZE) to the inlet-side target tension (ZE*) and/or the outlet-side target tension (ZA*) for a rear tension regulator which regulates the outlet-side actual tension (ZA) to the outlet-side target tension (ZA*).

9. The operating method as claimed in claim 1, wherein the resulting position target value (s*) is determined at least during the rolling of a central portion of the rolling stock by the use of a correction value (δs2*) determined by the use of an actual rolling force (F).

10. The operating method as claimed in claim 9, wherein the resulting base target value (s1*) is taken into account as part of the determination of the correction value (δs2*) in addition to the actual rolling force (F).

11. The operating method as claimed in claim 1, wherein the resulting position target value (s*) is determined at least during the rolling of a head of the rolling stock and/or a tail of the rolling stock without the use of an actual rolling force (F).

12. The operating method as claimed in claim 1, wherein the resulting position target value (s*) is determined by the use of the deviation of a thickness (d) of the rolling stock, measured at the outlet side of the roll stand, from a target thickness (d*).

13. A control system for a roll stand for rolling a flat rolling stock, wherein the control system is formed by hardware blocks and/or software programs in such a way that during operation it implements an operating method as claimed in claim 1.

14. A rolling unit for rolling flat metal rolling stock, wherein the rolling unit has a roll stand for rolling the flat rolling stock and a control system as claimed in claim 13.