EP1457274B1 - Method and device for avoiding vibrations - Google Patents

Abstract

Process for avoiding vibrations, especially 3- and 5-octave vibrations in a roll unit having a roll stand with provision for roll adjustment, a set of rolls, including a controller, with the aid of which the degree of adjustment, which changes with time, is determined in real time, an actuator, via which one roll of the roll set l is admitted (sic) and the degree of control is held at a specific desired value (sic) and the degree of control is held at a specific desired value. Independent claims are included for: (1) a device for avoiding the vibrations; (2) A band-like roll material of thickness variations at least 20% less than given thickness tolerances.

Description

The invention relates to a method and a device for avoiding vibrations, in particular 3rd and 5th octave oscillations, in a rolling mill with at least one roll stand with roll adjustment and at least one set of rolls.

In rolling mills, it is known that under certain operating conditions to undesirable vibrations or vibrations, which can lead to significant damage to the system, as well as defects in the rolled product. By superimposing vibrations whose causes have not yet been fully clarified in detail, resonating vibrations, ie vibrations with negative damping, can occur. A consequence of this is unstable vibration states or vibrations with a very high energy content. In addition to the aforementioned damage to the system, however, impermissible deviations in the geometric dimensions and undesirable surface patterns or surface defects on the rolling stock can also occur. Both costs are significant costs for the production because the defective rolled products must be rejected as scrap.

Those skilled in the art will recognize two typical groups from the plurality of vibrations occurring in rolling processes, which are classified according to their characteristics, e.g. the frequency and its effect are divided into 3rd and 5th octave oscillations. 3. Octave oscillations occur in a frequency range of about 100 to 350 Hz and are characterized by a very high energy content, so that considerable mechanical damage to the rolling mill can occur. These vibrations are accompanied by a loud noise. The specified frequencies depend on the particular system configuration and the rolling parameters and may therefore differ from this. At the set of rolls, an oppositely directed oscillation frequently occurs between the rolls, which leads to stretching of the frame stands. Stick-slip effects can be further causes for the vibrations, whereby also differences at the driving torques of the rollers can be cause of the vibrations. A special feature of these vibrations is the occurrence of unstable vibration states.

5th octave oscillations occur in a frequency range of about 500 to 800 Hz and lead to surface defects in the rolling stock and are sometimes only by this Defects detected at the rolling stock. The work rolls oscillate relative to the support rollers.

Both types of vibration have in common that it comes to movements of the set of rollers and thus to a deviation from the nominal roll gap. Depending on the type of vibration, the defects on the rolling stock show different manifestations as surface defects, as geometric defects or as combinations thereof.

Monitoring systems are known from the prior art. These systems observe or measure the vibration condition of the rolling mill or rolling stands and reduce the rolling speed in the event of vibrations, in order to reduce the vibrations or to avoid instabilities. A disadvantage of methods that use monitoring systems, is a significant productivity decline, due to a reduction of the rolling speed.

Furthermore, rolling mills with passive vibration damping systems are known. In this case, the energy of a vibration occurring is reduced by means of dampers and thus reduces the risk of damage. However, these systems can only insufficiently avoid surface defects on the rolling stock, so that the task of producing a fault-free rolling stock is not solved.

The US 5,724,846 describes a method for controlling vibrations (octave oscillations) in a rolling mill for rolling strip. In this case, the rolling mill is impressed on a vibration component, which is asynchronous relative to a vibration present in order to avoid vertical vibrations of the rollers. However, the described solution is always based on an existing vibration, which is used as the basis for the countermeasure. In rolling mills, this solution is not sufficient, as due to changing operating conditions despite the countermeasure may still occur on the rolled strip. In particular, for aufklingende oscillations, which are characterized by a negative damping, by the in the US 5,724,846 described invention no solution can be found.

From the US 6,387,214 B1 a device can be seen, wherein based on a measured vibration by means of an actuator, the vibration state of a roller is influenced. The solution only provides an indication of how the vibrations are reduced, but not how they can be avoided. In the case of unstable vibration states no solution is offered.

• Kailath T.: "Linear Systems", Prentice Hall, 1980 .
• Franklin G., Powell D., Emami-Naeini A.: "Feedback Control of Dynamic Systems", Fourth Edition, Prentice Hall, 2002 .
• Vidyasagar M.: "Nonlinear Systems Analysis", Second Edition, Prentice Hall, 1993 .

It is a fundamental feature that unstable vibration states can only be eliminated and thus stabilized by regulations, ie by feedback of the information signal. A detailed explanation of this fact can be found in the publications below:

• Kailath T .: "Linear Systems", Prentice Hall, 1980 ,
• Franklin G., Powell D., Emami-Naeini A: Feedback Control of Dynamic Systems, Fourth Edition, Prentice Hall, 2002 ,
• Vidyasagar M .: "Nonlinear Systems Analysis", Second Edition, Prentice Hall, 1993 ,

It is an object of the invention, a method according to the preamble of claim 1, to further develop so that damage to the rolling mill or defects in the rolling stock due to vibrations or avoided or excluded.

The object is achieved according to the inventive method according to the characterizing part of claim 1. By the method according to the invention, the generation of vibrations, which can lead to disruptions of the rolling operation or to defects in the rolling stock, avoided and ensured a vibration and trouble-free operation. On the basis of at least one permanently measured variable representing a controller having a mathematical control law based on a system of linear and nonlinear equations and / or differential and / or difference equations and submodels characterizing the condition of the plant with a hydraulic and / or mechanical and / or or a rolling force model, supplied, is determined by means of this controller in real time at least one variable variable manipulated variable, at least one actuator (5) supplied and acted upon by the actuator at least one of the rolls of the set and / or the rolling stock, the controlled variables Comparison of the measured quantities with the target values are kept permanently at defined setpoints.

In order to predict the behavior of the controlled system, in addition to a sufficiently precise detection of the operating state, a precise description of the system or of the system behavior is necessary. The system behavior is described by a mathematical description, which takes into account all relevant physical influences and relationships and the material behavior of plant components and rolling stock, by linear or non-linear or combinations of linear and non-linear submodels, whereby a sufficiently accurate simulation for the controlled system is achieved ,

By taking into account the essential system nonlinearities, such as the rolling force model, actuator, etc., the controller is deprived of the energy that leads to the vibration, or it reaches the minimum energy stored in the system rolling mill. With the mathematical control law, the manipulated variable (s) is determined as a function of the measured variable (s) based on linear and / or nonlinear equations and / or differential equations and / or difference equations. A control scheme is in Fig. 1 shown.

In the case of unstable operating points, the energy stored in the system and thus also the amplitudes of the oscillations increase in the course of time. Without affecting the system by a targeted control intervention, or as in known systems by reducing the belt speed, belt cracks, severe damage to the system, system downtime and thus very high costs can occur. By reducing the belt speed it is achieved that the system becomes stable again and the amplitude decreases, but under the disadvantage of a reduced productivity already described.

According to the assemblies and the system behavior, the submodels include a hydraulic and / or a mechanical and / or a rolling force model. By means of the partial models, the rolling mill is adequately described and mapped in the control law, whereby in addition to the behavior of the plant parts and the plant load the behavior of the entire rolling mill is mapped with high accuracy.

• Kugi A.: "Nonlinear Control Based on Physical Models", Lecture Notes in Control and Information Sciences 260, Springer, 2000 .
• Merritt H. E.: "Hydraulic Control Systems", John Wiley & Sons 1967 .

One possible hydraulic sub-model is described in detail in the publication below.

• Kugi A .: "Nonlinear Control Based on Physical Models", Lecture Notes in Control and Information Sciences 260, Springer, 2000 ,
• Merritt HE: "Hydraulic Control Systems", John Wiley & Sons 1967 ,

• Kugi A., Schlacher K., Keintzel G.: "Position Control and Active Eccentricity compensation in Rolling Mills", at - Automatisierungstechnik S. 342-349, Oldenbourg, 1999 .

Further descriptions of possible models for hydraulics and for rolling force determination can be found in the publication:

• Kugi A., Schlacher K., Keintzel G .: "Position Control and Active Eccentricity Compensation in Rolling Mills", at - Automatisierungstechnik S. 342-349, Oldenbourg, 1999 ,

• Grabmair G., Schlacher K., Kugi A.: "Coupling effects in multi stand rolling mills", Metal Forming 2000, pp. 295-301, 2000 .
• Bland D., Ford H., Ellis F.: "Cold rolling with strip tension", Part I, Journal of the Iron and Steel Institute, pp. 57-72, 1951 .
• Bland D., Ford H., Ellis F.: "Cold rolling with strip tension", Part II, Journal of the Iron and Steel Institute, pp. 239-245, 1952 .
• Bland D., Ford H.: "Cold rolling with strip tension", Part III, Journal of the Iron and Steel Institute, pp. 245-249, 1952 .
• Jortner D., Osterle J., Zorowski C.: "An analysis of cold strip rolling, Int. J. Mech. Sci., Vol.2, pp. 179-194, 1960 .

Detailed references to the rolling force models and the specific tasks for coupled rolling stands in rolling mills can be found in the references:

• Grabmair G., Schlacher K., Kugi A .: "Coupling effects in multi stand rolling mills", Metal Forming 2000, pp. 295-301, 2000 ,
• Bland D., Ford H., Ellis F .: "Cold Rolling with Strip Tension", Part I, Journal of the Iron and Steel Institute, p. 57-72, 1951 ,
• Bland D., Ford H., Ellis F .: "Cold Rolling with Strip Tension", Part II, Journal of the Iron and Steel Institute, p. 239-245, 1952 ,
• Bland D., Ford H .: "Cold Rolling with Strip Tension", Part III, Journal of the Iron and Steel Institute, p. 245-249, 1952 ,
• Jortner D., Osterle J., Zorowski C .: "An analysis of cold strip rolling, Int. J. Mech. Sci., Vol.2, pp. 179-194, 1960 ,

In conjunction with the control law, it is possible to determine one or more manipulated variables on the basis of a precise prediction of the system behavior and to influence the operating state of the rolling plant via at least one actuator such that the formation of third and fifth octave oscillations for all operating states the system can be prevented. This ensures that, for example, for high rolling speeds and low Walzgutdicken the formation of octave vibrations is prevented.

Due to the permanent monitoring of the system status, at least one permanently measured variable, a continuous supply of the size to the controller and the determination of at least one temporally variable manipulated variable in real time, a permanent monitoring and a permanent intervention in the system behavior is achieved. Due to the application of the system via at least one actuator, the oscillatory system is constantly deprived of energy, so that the formation or the formation of octave oscillations is reliably prevented. The measured quantity is used as an indicator for the plant condition and kept at defined values.

According to a particular embodiment, the vertical acceleration of the set of rolls is used as the measured variable. The vertical acceleration has proved to be a good indicator of the state of vibration in the rolling stand, as this information about the current motion situation of the rollers and thus the load roll gap is given. The operating status can be recorded precisely and inexpensively via a simple measuring installation.

Another simple embodiment of the invention provides as a measured size, the use of the cylinder pressure of the roller adjustment. As a result of this embodiment, the current operating state is mapped very well via the cylinder pressures, for example the setting cylinder, so that an exact prediction of the system behavior and control action can be used to avoid octave oscillations on the basis of the measurement.

In a particular embodiment of the method, the vertical position of the piston of the roller adjustment is used as the measured variable. Since the vertical position of the set of rollers or the rollers of the set of rollers define the Lastwalzspalt, the vibration behavior is well derivable from deviations from a setting position.

Another embodiment is achieved by using the state of tension in the rolling stock as measured size. Thus, in particular, the coupling of the stands of the rolling mill on the rolling stock and the overlapping vibrations is mapped in the rolling stands.

In a preferred embodiment of the method according to the invention, a plurality of permanently measured variables are used as input variables for the controller. By combining two or more measured variables, the current operating status is recorded very precisely so that the best possible influence on the vibration behavior is achieved via the controlled system. Combinations of at least two measured quantities, e.g. the vertical acceleration and / or the cylinder pressure of the roll adjustment and / or the vertical position of the piston of the roll adjustment and / or the tensile state used in the rolling stock, the design is selected according to the needs of the rolling mill. An adaptation of the control according to the invention to the respective plant situation is thus even more precisely possible.

In a further embodiment of the method according to the invention, the loading of the roller of the set of rollers takes place in the one or more Anstellrichtungen of the set of rollers. By this measure, we directly targeted the vibration behavior and thus the load roll gap achieved. It is also advantageous to use the existing employment in the respective scaffolding, additional units can be avoided.

An extension of this inventive concept for applications with particularly high demands is achieved by applying the roller of the set of rolls in several directions. Since the third and fifth octave oscillations can not be assigned to a single direction of movement, but cause three-dimensional action, the action of the actuators in several directions allows an even more efficient avoidance of vibrations. In particular, a solution for a control method for avoiding 3rd and 5th octave oscillations is therefore given for any roll arrangements or roll stand configurations.

A particularly advantageous embodiment of the method provides for the application of at least one roller over the adjusting device of the set of rollers. Due to this feature, a very simple and inexpensive solution is found by the coupling of employment and intervention to avoid vibrations in a superimposed process.

Another possible embodiment of the method according to the invention provides for loading of the roller via the axial roller displacement device of the roller set. By using a standard existing in many rolling stands, actuator, a very simple solution can be found. By combining this solution with an action on the roller adjustment a very flexible solution is achieved, which is all the requirements.

The inventive method provides for the avoidance of 3rd and 5th octave oscillations by a permanent reduction of the vibration energy, ie a continuous energy dissipation from the oscillatory system rolling stand, in particular the set of rollers before. The continuous energy dissipation ensures that no vibrations or vibrations, in particular those with a high energy content form, which can lead to considerable damage to the system or even to defects in the rolling stock.

A particular embodiment provides for the reduction of vibrations, in particular in the setting direction of the rollers. This simplified solution disregards oscillations with a direction other than the setting direction. This will be a simple Solution found for the method that meets the demand for safe avoidance of 3rd and 5th octave oscillations.

The device according to the invention for avoiding vibrations, such as e.g. 3rd and 5th octave oscillations, in a rolling mill with at least one roll stand with roll adjustment and at least one set of rolls comprises at least one measuring device, for permanently measuring a size of the rolling mill, a controller that a mathematical control law based on a system linear and non-linear Equations and / or differential and / or differential equations, and the plant state characterizing sub-models with a hydraulic and / or mechanical and / or a rolling force model includes, the measured size can be supplied, with the help of this controller in real time at least one variable variable manipulated variable can be determined, and further at least one actuator to which the manipulated variable can be supplied and on the at least one of the rollers of the set of rollers and / or the rolling load can be acted upon / is wherein the hydraulic cylinder of the roller adjustment is additionally acted upon to avoid vibrations.

This simple structure is a cost-effective solution found that largely relies on robust and reliable components. As a result of the regulator solution according to the invention, it is achieved that the rolling system exhibits the desired behavior predefined by the desired value.

According to a particular embodiment, a hydraulic actuator is used as the actuator. By combining with existing in scaffolding, further hydraulic actuators, such as. The hydraulic roller adjustment or the axial roller displacement is a robust and safe solution with high flexibility, regardless of the type of plant achieved.

Another particular embodiment provides a piezoelectric actuator as an actuator, which is characterized by high dynamics and high energy density, so that a very high precision in the control action is achieved. The actuator is installed in the rolling mill in such a way that dynamic, but not static, loads can act on the piezoelectric actuator. This ensures that overloads can not lead to damage to the piezoelectric actuator.

A particularly advantageous embodiment of the device is achieved by the combination of different actuators, since the different characteristics of the actuators partial frequencies can be covered very well.

Vibrations or vibrations represent a disruptive effect for rolling processes, which is reflected as a defect in the rolling stock. In most cases, surface defects and thickness deviations occur on the rolling stock.

Deviations from the nominal thickness of the rolling stock cause great costs, as always a minimum thickness must be guaranteed by the manufacturer. All positive thickness deviations, ie thicknesses greater than the guaranteed minimum thickness, thus represent a very significant cost factor, since this must be allocated to the total production quantity of the rolling mill. A reduction in the thickness deviations, ie narrower thickness tolerances, means a very high saving potential for the rolling mill operator. For many further processing steps cause excessive variations in thickness of the rolling stock, especially during forming, unacceptable disturbances, so that larger thickness deviations make a separation of the rolling required. This leads to very high scrap costs.

By applying the method according to the invention and the device to rolling processes for the production of rolling stock, an overall more stable rolling process is achieved in addition to the avoidance of damage to the system and defects in the rolling stock. As a result, narrower thickness tolerances can be maintained on the rolling stock and failures due to surface defects can be avoided. Thickness tolerance is understood to mean those rolling stock thicknesses which represent a permissible deviation from a desired thickness, that is to say do not exceed certain predefined deviations. Usual details are given as a percentage of the rolling stock thickness or in absolute terms with the permissible deviations in ± amount from the nominal thickness, the data often being given in μm.

The achievable thickness tolerances represent a significant development step, since they can not be represented with currently available methods and devices.

Compared to the state of the art, it is possible to set thickness tolerances, which are at least 20% tighter than today's technically usual tolerances, such as in tandem cold rolling mills, due to the more stable rolling conditions. Tab. 1 shows typical thickness tolerances of a tandem cold rolling mill. These thickness tolerances apply to strip-shaped rolling stock, with the exception of short sections on the strip head and on the strip foot, the lengths of these sections being specified by guarantee formulations which take into account the specific nature of a plant and can therefore vary. strip thickness tolerance 0.25 - 0.50 mm ± 1.2% 0.50 - 0.89 mm ± 1.0% 0.89 - 1.60 mm ± 0.9% 1.60 - 2.54 mm ± 0.8%

Especially for thin and wide tapes, which provide the highest technological requirements, the solution according to the invention offers a completely new idea and technical embodiment compared with the state of the art.

• Fig.: 1 Regelschema der Regelstrecke
• Fig.: 2 Anlagenschema

The invention is explained below by way of example with reference to FIGS.

• Fig .: 1 Control scheme of the controlled system
• Fig .: 2 system diagram

FIG. 1 shows the basic structure of the controlled system, which does not deal with the controller mathematics or the submodels.

About sensor or the necessary sensor 1 sizes 2 of the rolling mill are detected. These measured quantities 2 are fed to a controller 3. The controller 3 contains a mathematical control law and the system state characterizing partial models. With the aid of the controller 3, at least one temporally variable manipulated variable 4 is determined in real time and supplied to the actuator 5. By the actuator 5 is a loading of the rolling mill (the route) 6, wherein the vibration state of the rolling mill 6 is selectively influenced. Exposing disturbances 7 are taken into account via the measured quantities 2. In a comparison of the measured variables 2 with the desired values 8, the setting of the desired state or the control intervention in the oscillatory system of the rolling mill 6 takes place.

In Fig. 2 a framework of a rolling mill 6 is shown with the schematically indicated major components. Via a regulator 3 and a servo valve 12, an actuator 5, here indicated as a hydraulic cylinder, acted upon. Thus, in addition to the adjusting movement and the admission to avoid vibrations. As input variables for a controller 3, signals of a displacement or position measurement 9, a pressure measurement 10 or an acceleration measurement 11 with an acceleration sensor 13 are indicated. In addition, input variables that affect the rolling stock, such as stress conditions in the rolling stock 14,15 or combinations of these sizes are used. To determine the states of stress in the rolling stock, for example measuring devices, not shown here, which measure contact with the rolling stock, can be used. Actuators for acting example of the hydraulic cylinder are not shown here in detail, the corresponding arrangement is for the skilled person, however, due to its knowledge, no problem. In one possible embodiment, as shown here, the hydraulic cylinder for roll adjustment is additionally applied to avoid vibrations.

Claims (15)

1. Method for the avoidance of oscillations, in particular 3rd and 5th octave oscillations, in a rolling mill with at least one roll stand having roll adjustment and with at least one roll set, characterized in that at least one permanently measured variable of the rolling mill is fed to a controller (3), which comprises a mathematical control law based on a system of linear and non-linear equations and/or differential and/or difference equations and submodels characterizing the mill state and having a hydraulic and/or mechanical and/or rolling-force model, at least one time-variable manipulated variable (4) is determined in real time with the aid of this controller (3) and is fed to at least one actuator (5), and at least one of the rolls of the roll set and/or the rolling stock is acted upon by the actuator (5), the control variables being held permanently at defined desired values by a comparison of the measured variables with the desired variables.
2. Method according to Claim 1, characterized in that the vertical acceleration of the roll set is used as a measured variable.
3. Method according to one of the preceding claims, characterized in that the cylinder pressure of the roll adjustment is used as a measured variable.
4. Method according to one of the preceding claims, characterized in that the piston position of the roll adjustment is used as a measured variable.
5. Method according to one of the preceding claims, characterized in that the tensile-stress state in the rolling stock is used as a measured variable.
6. Method according to one of the preceding claims, characterized in that combinations of the vertical acceleration and/or of the cylinder pressure of the roll adjustment and/or of the vertical position of the roll set and/or of the tensile-stress state are used as measured variables.
7. Method according to one of the preceding claims, characterized in that action upon the roll of the roll set takes place in the adjustment direction.
8. Method according to one of the preceding claims, characterized in that action upon the roll of the roll set takes place in a plurality of directions.
9. Method according to one of the preceding claims, characterized in that action upon the roll takes place via the adjustment device of the roll set.
10. Method according to one of the preceding claims, characterized in that action upon the roll takes place via an axial roll displacement device of the roll set.
11. Method according to one of the preceding claims, characterized in that the energy content of oscillations is continuously reduced and/or eliminated in the adjustment direction by means of permanent action upon the roll.
12. Device for the avoidance of oscillations, in particular 3rd and 5th octave oscillations, in a rolling mill with at least one roll stand having roll adjustment and at least one roll set, for carrying out the method according to one of Claims 1 to 13, characterized in that at least one measuring device (9, 10, 11) for the permanent measurement of a variable of the rolling mill and a controller (3), which comprises a mathematical control law based on a system of linear and non-linear equations and/or differential and/or difference equations and submodels characterizing the mill state and having a hydraulic and/or mechanical and/or rolling-force model, to which the measured variable (2) can be fed, are provided, and at least one time-variable manipulated variable (4) can be determined in real time with the aid of this controller (3), and, further, comprises at least one actuator (5), to which the manipulated variable (4) can be fed and via which at least one of the rolls of the roll set and/or the rolling stock can be acted upon, the hydraulic cylinder of the roll adjustment being additionally acted upon for the avoidance of oscillations.
13. Device according to Claim 14, characterized in that the actuator (5) is designed as a hydraulic and/or servo-hydraulic actuating element.
14. Device according to Claim 14, characterized in that the actuator is designed as a piezoelectric actuating element.
15. Device according to Claims 14 to 16, characterized in that the actuator comprises combinations of various actuating elements.

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