EP0638375B1 - Method and device for monitoring chattering in twin drives of tolling stands - Google Patents

Description

In the case of a twin drive on a roll stand, the upper roll and the lower roll of the roll stand are driven separately by an upper and a lower motor. The coupling of each motor via a more or less torsionally rigid shaft to the associated roller results in a structure capable of torsional vibrations. Strong changes in the friction values in the roll gap can start a self-excitation process, the rotational energy supplied to the rolls being converted into torsional vibration energy. The mechanical torsional vibration behavior of the twin drive is damped in such a way that the speed control for the motors can no longer stabilize sufficiently. If the adhesion between the two rollers is lost, slipping processes and, as a result, the so-called rattling start.

It is known to detect rattling by detecting vibrations of the drives and monitoring them for exceeding a predetermined amplitude. If the amplitude is exceeded, a chatter detection signal is generated which is given to the speed control in the sense of a reduction in the speed until the rattling stops. However, operational vibrations caused by the tapping in the roll stand must not trigger the chatter monitor to respond. So far, the well-damped tapping vibrations could only be selected via the amplitude threshold of chatter vibrations. In many cases, however, the remaining time for a reaction is too short, so that drive damage can occur.

The invention is therefore based on the object of enabling a quick and reliable differentiation between operational tapping vibrations and chatter vibrations.

According to the invention, the object is achieved by a method for chatter monitoring in twin drives of rolling stands, in which vibrations of the upper drive and vibrations of the lower drive are detected, the detected vibrations are monitored for exceeding a predetermined amplitude, in the event of an amplitude exceeding a chatter detection signal is generated and at furthermore, the frequencies of the vibrations of the upper drive and the lower drive are monitored for equality and, in the event of a frequency equality, the chatter detection signal is suppressed.

In a corresponding manner, the object is achieved by a device for chatter monitoring in twin drives of rolling stands with a device for detecting vibrations of the upper drive, with a device for detecting vibrations of the lower drive, with a device for monitoring the detected vibrations for exceeding a predetermined amplitude and for generating a chatter detection signal when the amplitude is exceeded and with a device for monitoring the frequencies of the detected vibrations for equality and for suppressing the chatter detection signal in the event of frequency equality.

The invention takes advantage of the phenomenon that operational tapping vibrations and chatter vibrations differ in their natural frequencies. In the case of a normal tapping, the upper and lower rollers adhere to one another so that both rollers vibrate at a common natural frequency due to the mechanical coupling. If, on the other hand, slipping occurs and liability is lost, the upper and lower rollers and the associated drives vibrate with their own natural frequencies, the natural frequencies of the upper drive and lower drive being different because of the generally unequal length of the drive shafts.

The amplitude and frequency monitoring of the detected vibrations takes place in an advantageous manner in that vibration-influenced measured variables, such as. B. the drive speed or the drive torque of the upper drive and vibration-influenced measured variables of the lower drive each an arrangement of bandpass filters with staggered center frequencies in the natural frequency range of the drives that the output signals of the bandpass filter are monitored for exceeding the predetermined amplitude and that to monitor the vibrations of the upper drive and of the sub-drive for frequency equality, the output signals of all bandpass filter pairs with bandpass filters for the top drive and the bottom drive and corresponding center frequency are compared. The subdivision of the natural frequency ranges of the two drives by means of the bandpass filter into a grid of frequency intervals enables a very fast frequency comparison of the vibrations of the two drives without great circuitry or computational effort. The output signals of each pair of bandpass filters are preferably monitored for the joint exceeding of a limit value. As an alternative to this, the output signals of each pair of bandpass filters can be subtracted from one another, the difference signal thus obtained being monitored for a limit value being exceeded.

To determine the frequency equality of the vibrations of the upper drive and the lower drive, an evaluation is carried out, preferably an AND operation of all limit value violations detected in the bandpass filter pairs. Alternatively, the limit value can also be evaluated characterized in that with a predetermined number of bandpass filter pairs with center frequencies in a predetermined relation to each other, for. B. immediately adjacent center frequencies, a limit violation must be detected in order to derive a frequency equality of the considered vibrations.

In order to increase the speed of detection when vibrations occur, it is provided that the output signal of each bandpass filter is rectified and differentiated in parallel, rectified, multiplied by the reciprocal of the center frequency of the bandpass filter and then added to the rectified output signal.

The amplitude monitoring of the detected vibrations is carried out in the simplest manner in that the output signal with the greatest amplitude is selected from the output signals of the bandpass filter and used to monitor whether the predetermined amplitude has been exceeded.

In order to reduce or eliminate the chatter vibrations, the rolling speed is reduced when the chatter detection signal occurs until the slipping stops and the lost adhesion between the top and bottom rollers is restored. In this context, it is advantageously provided that the detected vibrations of the upper drive and the lower drive are monitored for exceeding different amplitudes, that when the lower amplitude is exceeded there is a ramp-like reduction in the rolling speed and when the higher amplitude is exceeded there is a sudden reduction in the rolling speed .

FIG 1

ein Beispiel für einen Zwillingsantrieb an einem Walzgerüst,

FIG 2

ein Ausführungsbeispiel in Form eines Blockschaltbildes für die erfindungsgemäße Erzeugung zweier Ratterdetektionssignale für unterschiedlich starke Ratterschwingungen und

FIG 3

ein Ausführungsbeispiel für die Realisierung der Walzgeschwindigkeitsreduzierung in Abhängigkeit von den Ratterdetektionssignalen,

FIG 4

eine zu dem in FIG 2 gezeigtes Ausführungsbeispiel alternative Ausführungsform und

FIG 5

ein Ausführungsbeispiel für die Erhöhung der Ansprechgeschwindigkeit beim Auftreten von Schwingungen.

To explain the invention, reference is made below to the figures of the drawing; show in detail

FIG. 1

an example of a twin drive on a roll stand,

FIG 2

an embodiment in the form of a block diagram for the inventive generation of two chatter detection signals for different strength chatter vibrations and

FIG 3

an embodiment for the realization of the rolling speed reduction depending on the chatter detection signals,

FIG 4

an alternative to the embodiment shown in FIG 2 and

FIG 5

an embodiment for increasing the response speed when vibrations occur.

1 shows a roll stand 1 with two work rolls, namely an upper roll 2 and a lower roll 3, and associated supporting rolls 4 and 5. The upper roll 2 and the lower roll 3 are driven by a twin drive, in which two separate motors 6 and 7 via drive shafts 8 and 9 and universal joints 10 are connected to the upper roller 2 and the lower roller 3. Since the universal joints 10 can only compensate for a limited angle, the center distance in the two motors 6 and 7 must be kept small in order to limit the length of the drive shafts 8 and 9. The size of the two motors 6 and 7 therefore requires an offset arrangement of the two motors 6 and 7.

The circuit shown in FIG. 2 for the detection of chatter vibrations is fed at a point 11 with a measurable variable M _{o which} can be influenced by vibrations of the upper drive and at a point 12 with a vibrated measured variable M _{u of} the lower drive. The measured variables M _o and M _u can be, for example, the speed, the torque or the drive current act in engines 6 and 7. The measured variable M _{o of} the top drive is fed to a plurality of bandpass filters 13 with different center frequencies staggered between the minimum and maximum natural frequency of the twin drive. Each of the bandpass filters 13 is followed by a link 14 for forming the amount of the bandpass filter signals and a link 15 for signal smoothing. The measured variable M _{u of} the lower drive is also fed to a number of bandpass filters 16, the center frequencies of which are staggered in the same way as for the bandpass filters 13. The band filters 16 are also each followed by a link 17 for forming the amount of the bandpass filter signals and a link 18 for signal smoothing. The smoothed amounts of the bandpass filter signals at the outputs of the elements 15 and 18 are fed to a maximum value detector 19, which selects and switches on the maximum of the input signals fed to it. The maximum value detector 19 is followed by two threshold value detectors 20 and 21, each of which generates an output signal when the maximum value supplied to them exceeds a predetermined threshold value. The threshold value detector 20 is set to a lower threshold value and the threshold value detector 21 is set to a higher threshold value. The output signal of the threshold value detector 20 is fed to an AND gate 22 and that of the threshold value detector 21 to a further AND gate 23.

If vibrations occur within the twin drive, the vibration maximum contained in the frequency spectrum of the vibrations is monitored for exceeding two different amplitudes. If the lower amplitude is exceeded, a chatter detection signal R1 is generated at the output of the AND gate 22 and a further chatter detection signal R2 is generated at the output of the AND gate 23 if the additional condition is met that the current speeds of the twin drive are met exceed a predetermined value and that the vibrations detected are not operational tapping vibrations.

For this purpose, the speeds n _o and n _{u of} the upper drive and the lower drive are fed to the circuit at points 24 and 25. The speeds n _o and n _u are monitored after the amount has been formed in amount-forming elements 26 and 27, regardless of the direction of rotation in limit value indicators 28 and 29, for exceeding a limit, for example 5% of the maximum speed. Each of the two limit indicators 28 and 29 is connected at its output to the two AND gates 22 and 23.

To differentiate between chatter vibrations and operational tapping vibrations, each of the individual elements 15 and 18 for signal smoothing is followed by a limit value detector 30 or 31, which then generates an output signal when the smoothed amount of the bandpass filter signal has a limit value, for example 5% of the amount of the measured variables M _o or M _u . The outputs of two limit detectors 30 and 31, one of which is assigned to a bandpass filter 13 for the upper drive and the other to a bandpass filter 16 with the same center frequency for the lower drive, are each followed by an antivalence element (exclusive OR) 32, which then outputs an output signal generated when only one of the two limit detectors 30 and 31 reports that the limit has been exceeded. The outputs of the antivalence gates 32 are fed to an OR gate 33, which is connected on the output side to each of the two AND gates 22 and 23. So if in any of the staggered frequency intervals defined by the bandpass filter pairs 13, 16, the vibrations for the one drive, z. B. the top drive, exceed the limit, while in the same frequency interval for the other drive, z. B. the underdrive, no vibrations exceeding the limit value are detected, this indicates that there is no liability between the upper roller 2 and the lower roller 3, so that the upper and lower drive vibrate independently of one another with different natural frequencies. In this case, the generation of the chatter detection signals R1 and R2 is released. If, on the other hand, limit violations are detected in all frequency intervals both for the vibrations of the upper drive and for the vibrations of the lower drive, this indicates that the upper and lower drives vibrate together with the same natural frequency. In this case, there are operational tapping vibrations, so that the generation of the chatter detection signals R1 and R2 is suppressed.

umgewandelt wird.As FIG 3 shows, the chatter detection signal R1, which is generated when the chatter vibrations exceed the lower threshold value of the threshold value detector 20, is used to switch an integrator 34 on and off. A direction of rotation signal D is fed to the integrator 34 on the input side, which signal has the value +1 or -1 depending on the rolling direction or direction of rotation of the twin drive. The integrator 34 generates a ramp-shaped output signal with an increasing or decreasing ramp from this direction of rotation signal D, the level of the output signal being limited in a subsequent stage 35. If the detected chatter vibration exceeds the higher threshold value of the threshold value detector 21, a stepped output signal is generated with the help of a controllable switch 36, the value of which jumps from 0 to 1 or from 0 to -1 depending on the rolling direction. The output values of the integrator 34 and the controllable switch 36 are added in a summing element 37 to a speed correction value Δn, with which the speed setpoint n * for the twin drive is converted into a corrected speed setpoint ${\text{n}}_{}$${}_{\text{1}}\text{* = n * (1 + Δn)}$

is converted.

When chatter vibrations occur, the rotational speed for the twin drive is reduced either in the form of a ramp or jump, depending on whether the detected chatter vibrations exceed the lower or the higher threshold value.

FIG. 4 shows a circuit variant that differs from the circuit shown in FIG. 2 only in that, instead of the limit indicators 30, 31 and antivalence elements, 32 subtractors 38 with subordinate amount-forming elements 39 and limit indicators 40 are provided. The rectified and smoothed output signals of the bandpasses 13 and 16 assigned to the upper and lower drive with a matching center frequency are subtracted from one another, the difference signal obtained in this way being monitored after its rectification for exceeding a limit value.

5 shows an example of the increase in the response speed of the circuits shown in FIG. 2 and FIG. 4 with respect to the occurrence of vibrations. For this purpose, the output signal of each bandpass filter 13 or 16 is additionally differentiated in a differentiating element 41, rectified in an amount-forming element 42 and multiplied in a multiplier 43 by the reciprocal of the respective center frequency ω _{BP of} the bandpass filter 13 or 16 before it is added in a summing element 44 is added to the rectified output signal of the bandpass filter 13 or 16. As a result, the ripple of the signal at the input of the signal smoothing element 15 or 18 is reduced, so that the smoothing effect and thus the signal delay of the signal smoothing element 15 or 18 can be reduced.

Claims (11)

1. Method for chatter monitoring in twin drives of roll stands (1), where oscillations of the upper drive (2, 4, 6, 8) and oscillations of the lower drive (3, 5, 7, 9) are detected, the detected oscillations are monitored for the exceeding of a specified amplitude, in the event of the amplitude being exceeded a chatter detection signal (R1, R2) is generated and where, moreover, the frequencies of the oscillations of the upper drive (2, 4, 6, 8) and of the lower drive (3, 5, 7, 9) are monitored for equality and in the event of frequency equality the chatter detection signal (R1, R2) is suppressed.
2. Method according to claim 1, characterized in that measured variables (M_o) of the upper drive (2, 4, 6, 8) influenced by oscillation and measured variables (M_u) of the lower drive (3, 5, 7, 9) influenced by oscillation are in each case supplied to an arrangement of bandpass filters (13, 16) with mid-frequencies staggered in the natural-frequency range of the drives, in that the output signals of the bandpass filters (13, 16) are monitored for the exceeding of the specified amplitude and in that to monitor the oscillations of the upper drive (2, 4, 6, 8) and the lower drive (3, 5, 7, 9) for frequency equality the output signals of all bandpass filter pairs with bandpass filters (13, 16) for the upper drive (2, 4, 6, 8) and the lower drive (3, 5, 7, 9) and with corresponding mid-frequency are compared with each other.
3. Method according to claim 2, characterized in that to monitor the oscillations of the upper drive (2,4,6,8) and the lower drive (3,5,7,9) for frequency equality the output signals of each bandpass filter pair (13, 16) are monitored for the common exceeding of a limiting value.
4. Method according to claim 2, characterized in that to monitor the oscillations of the upper drive (2,4,6,8) and the lower drive (3,5,7,9) for frequency equality the output signals of each bandpass filter pair (13,16) are subtracted one from the other and the differential signal obtained in this way is monitored for the exceeding of a limiting value.
5. Method according to claim 3 or 4, characterized in that to determine the frequency equality of the oscillations of the upper drive (2, 4, 6, 8) and the lower drive (3, 5, 7, 9) there is an evaluation, in particular an AND operation, of all cases of limiting-value exceeding detected with the bandpass filter pairs (13, 16).
6. Method according to one of claims 2 to 5, characterized in that of the output signals of the bandpass filters (13, 16) that output signal with the greatest amplitude is selected and used to monitor for the exceeding of the specified amplitude.
7. Method according to one of claims 2 to 6, characterized in that the output signal of each bandpass filter (13, 16) is rectified and, in parallel therewith, is differentiated, rectified, multiplied by the reciprocal value of the mid-frequency (ω_BP) of the bandpass filter (13, 16) and subsequently added to the rectified output signal.
8. Method according to one of the preceding claims, characterized in that with the occurrence of the chatter detection signal (R1, R2) the rolling speed (n) is reduced.
9. Method according to claim 8, characterized in that the detected oscillations of the upper drive (2, 4, 6, 8) and the lower drive (3, 5, 7, 9) are monitored for the exceeding of different amplitudes, in that in the event of the exceeding of the respectively lower amplitude a ramp-like reduction of the rolling speed (n) takes place and in the event of the exceeding of the respectively higher amplitude a step-like reduction of the rolling speed (n) takes place.
10. Device for chatter monitoring with twin drives of roll stands with a device to detect oscillations of the upper drive (2, 4, 6, 8), with a device to detect oscillations of the lower drive (3, 5, 7, 9), with a device (20, 21) to monitor the detected oscillations for the exceeding of a specified amplitude and to generate a chatter detection signal (R1, R2) upon amplitude exceeding and with a device (13 to 18), (30 to 33) to monitor the frequencies of the detected oscillations for equality and to suppress the chatter detection signal (R1, R2) in the event of frequency equality.
11. Device according to claim 10, characterized in that the devices to detect the oscillations in each case have an arrangement of bandpass filters (13, 16) with staggered mid-frequencies.

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