Abstract:
A system and a method for measuring and determining flatness of a strip ( 1 ) of rolled material. Said system is comprising a measuring roll ( 2 ) having a cylindrical central structure ( 41 ) having a number of measuring devices for force/pressure registration. Said devicesis generating measurement output signals (U pi ) depending on the contact between the strip and the measuring roll ( 2 ), wherein said measurement output signal (U pi ) comprises a force component signal (U Fi ). Said system also comprises a Flatness Determination Unit ( 56 ), said unit being arranged for calculating the flatness (Δσ 1 ) of the strip based exclusively on signals derived from measurement output signal (U pi ) values generated by said measuring devices and information about the values of the width and thickness of the strip ( 1 ). The system is continuously determining the Wrap Angle (α) from at least one measurement output signal (U pi ) and automatically compensating for a changing Wrap Angle (α). The present invention also provides a computer program product, a computer data signal and a flatness determination signal for accomplishing said objects of the invention.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is related to provisional application Serial No. 60/272,051, filed Mar. 1, 2001, the teachings of which are incorporated herein by reference. 
     
    
     
       TECHNICAL AREA  
         [0002]    The invention relates to a measuring system and method for continuous production of substantially long and flat sheet or strip of material such as copper, steel or aluminium. More particularly it is a system, a computer program product, a computer data signal, a flatness determination signal and a method for flatness measuring for use in a rolling mill.  
         BACKGROUND ART  
         [0003]    In the rolling of strip and sheet materials it is common practice to roll a material to desired dimensions in a rolling mill stand and then feed the resulting strip to a coiler. On the coiler, the strip is wound up into a coil. Such coils are then taken off the coiler and after some time has elapsed moved on to subsequent processes such as annealing, slitting, or surface treatment processes and other processes.  
           [0004]    The tension in the strip between a mill stand and a coiler is carefully monitored and it is known to measure tension distribution across a strip in order to regulate the flatness of the rolled material. In U.S. Pat. No. 3,481,194 Sivilotti and Carlsson disclose a strip flatness sensor. It comprises a measuring roll over which the strip passes between a mill stand and, for this example, a coiler. The measuring roll detects the pressure in a strip at several points across the width of the strip. The pressure represents a measure of the tension in the strip. The measurements of tension in the strip result in a map of flatness in each of several zones across the width of the strip. U.S. Pat. No. 4,400,957 discloses a strip or sheet mill in which tensile stress distribution is measured to characterise flatness. The measures of flatness are compared to a target flatness and a difference between measured flatness and target flatness is calculated, as a flatness error. The flatness error is fed back via a control unit to the actuators of the mill stand, so as to regulate and control flatness in the strip in order to approach a zero flatness error.  
           [0005]    Different sensors, gauges and/or transducers, generates input values to a system for flatness measurement. Said system comprises different measurement systems or blocks for determining quantities like strip tension, distributed force and finally flatness.  
           [0006]    The quantity strip tension is a measured value corresponding to the force of the strip against the measuring roll. Said force is registered by means of tensiometer load cells, which are fixed at shaft bearings of the measuring roll. Strip tension is an important quantity for determining the average force on the roller and on each measuring device.  
           [0007]    Some necessary input quantities, like the wrap angle of the strip over the measuring roll, have not been determined by means of any measuring devices. They have been pre-loaded into the system and if a value is changing during the process it has been adjusted for an example, by calculation. In U.S. Pat. No. 3,481,194 Sivilotti and Carlsson prescribe a certain angle for the passing of the strip over the measuring roll. The wrap angle is an important value when calculating other values of interest. It is used for calculating the Distributed Force per sensor on the measuring roll. The wrap angle is depending on the radius of the coil on the coiler. The wrap angle will change when the radius of the coil is growing and, therefore, the value of the wrap angle has to be adjusted during the process.  
           [0008]    As shown above, prior art systems comprise different sensors for registering and measuring different quantities and, as a consequence thereof, different measurement blocks corresponding to said quantities. Said systems are quite complex and expensive. The cost for construction and support increases rapidly with growing complexity and increasing number of different systems and sensing devices like sensors and transducers.  
           [0009]    Thus, a system for measuring flatness having less different details, but still able to generate at least the same result as a prior art system, is preferable.  
         SUMMARY OF THE INVENTION  
         [0010]    It is an object of the invention to provide a flatness measuring system using measurement output signals only generated at the contact surface of a measuring roll and not elsewhere, e.g. at the shafts, for flatness determination and calculation. It is further an object of the invention to suggest a flatness measuring system comprising less number of different sensing devices and system blocks. It is another object of the invention to suggest a flatness measuring system and method wherein the wrap angle is continuously measured and determined. It is a further object of the invention to reduce the number of necessary input signals. It is a yet further object of the invention to provide a system and a method to measure the flatness of a strip. It is yet another object of the invention to provide a more correct value of the flatness.  
           [0011]    The invention may be described as a flatness measuring and determining system and method in which flatness of a given strip is of rolled material, comprising a measuring roll, having a number of force/pressure sensors/transducers that are situated in a certain pattern on said roll, each sensors/transducer generating an measurement output signal U pi depending on the pressure of the flat sheet on to the transducer/sensor and a Wrap Angle α of the strip on the measuring roll. Said system also comprises a flatness Determination unit, said unit being arranged for calculating a wrap angle value based on said measurement output signals, and, based thereon, the flatness of the strip. The present invention also provides a computer program product, a computer data signal and a flatness determination signal for accomplishing said objects of the invention.  
           [0012]    The main advantage of the invention is that the system contains a reduced number of different measuring blocks and different sensors/transducers.  
           [0013]    Another advantage is that the system is not so complex and expensive. A further advantage is that the system uses a measured value of the wrap angle and not an estimated value and therefore the system will provide a more correct value of the flatness. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    The present invention will be described in more detail in connection with the enclosed drawings.  
         [0015]    [0015]FIG. 1 (Prior art) shows schematically a part of a rolling mill including a flatness measuring roll, a mill stand and a coiler according to the known art.  
         [0016]    [0016]FIG. 2 (Prior art) shows a simplified block diagram for measuring flatness according to the known art.  
         [0017]    [0017]FIG. 3 illustrates a measuring roll.  
         [0018]    [0018]FIG. 4 shows a simplified block diagram of a preferred embodiment according to the invented system.  
         [0019]    [0019]FIG. 5 is a simplified block diagram of a Flatness Determination Unit, FDU, illustrating the blocks of the system and method steps according to the invention.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]    In order to explain the invention, a rolling mill system  10  in the prior art will first be described in summary detail. FIG. 1 (Prior art) shows a metal strip  1  passing through a mill stand  5  in a direction shown by an arrow D. Strip  1  passes over a measuring roll  2  to a coiler  3 . Measurement signals from the load cells at the shaft bearings of the measuring roll  2  are connected to the flatness measuring unit  4  via a first measurement connection  7 . Measuring devices on the measuring roll  2  are coupled to a flatness measuring unit  4  via a second measurement connection  8 . Measurements of the strip corresponding to strip flatness are taken on exit from mill stand  5  by measuring roll  2  before coiling the strip on coiler  3 .  
         [0021]    [0021]FIG. 2 (Prior art) shows a simplified block diagram for a known system for a flatness measuring unit  4 . Said system comprises a Strip Tension Measurement System  12 , a Distributed Force Measurement System  14  and a Flatness Measurement System  16 . The Strip Tension Measurement System (STMS)  12  is electrically connected to tensiometer load cells  18 , which are fixed at the shaft bearings  6  of a measuring roll  2 . The load cells  18  generates an input signal U Fload  that is transmitted over a first measurement connection  7  to the STMS. Said input signal U Fload  is a measured value corresponding to the force F L  of the strip against the measuring roll  2 . For calculating Strip Tension T, a value for the current wrap angle α of the strip over the roll  2  is needed. The wrap angle α changes with the increased radius of the coil and the system uses an estimate value α est  for the wrap angle. Said estimate value α est  and load cell generated value U Fload  is used for calculating the strip tension T [N]. The calculated value T is transmitted to Distributed Force Measurement System (DFMS) 14 . The measuring roll ( 2 ) has a number of force/pressure sensors/transducers that are situated in a certain pattern on said roll. Each sensor/transducer generates an measurement output signal U pi  depending on the pressure of the flat sheet on to the transducer/sensor. The measurement signals are transmitted to the DFSM  14  via the second measurement connection  8 . The DFSM  14  usesthe strip tension T and each sensor/transducer signal for determining the Distributed Force F 2  per sensor/transducer. The determined value F 2  is transmitted to Flatness Measurement System (FMS)  16  for determining the Measured Flatness Δσ [N/mm 2 ]. The width w and the thickness t, either a one- or multiple-dimensional vector, of the system has to be pre-loaded into the FMS.  
         [0022]    Flatness per zone across the width of the strip during rolling is determined by means of the measuring roll  2 , which has a number of force/pressure sensors that are situated in a certain pattern on said roll. A zone of the roll is a ring formed sector that is parallel with the rotational axle of the roller. Each measurement zone has at least one sensor/transducer and each sensor generates an measurement output signal depending on the pressure of the flat sheet on to the sensor/transducer. The sensors  22  are distributed on the roll in a special pattern.The flatness of the strip  1  will be mapped in parallel lines across the strip perpendicular to the movement direction. If there is a bump or irregularity in the strip, the sensors that come in contact with the bump will register a signal amplitude that differs from the average value generated from other parts of the strip.  
         [0023]    In FIG. 3 an embodiment of a measuring roll  2  is illustrated. It comprises a cylindrical central structure  41 , a strip contact device  42  and shaft taps  45 . The strip contact device  42  is tightly attached to the structure  41 , both having a circular cross-section. The strip contact device  42  of the measuring roll  2  is divided into a number of measurement zones 43 , i (i=1,2,3 . . . , n),. All measurement zones together define a measurement area of the measuring roll  2 . Each zone  43  may correspond to one strip contact ring and all rings together will constitute the strip contact device  43 . Each zone  43  is annular and comprises a number of sensors  22 . The sensors  22  are located in parallel slots  44 . The strip contact device  42  comprise metal rings that covers and protects the sensors. The end parts  46  of the measuring roll  2  have a shaft tap  45 .  
         [0024]    However, the invention is not limited in its use to this described embodiment of measuring roll.The measuring roll  2  may have the force/pressure sensors distributed and organized in any known or unknown pattern on said roll and the measurement zones may have another distribution along the roll. The borders of the zones may be crossing the sensors.  
         [0025]    A preferred embodiment according to the invented system will now be described by means of FIG. 4.  
         [0026]    Measuring devices comprises force/pressure transducers/sensors/gauges of known types will in the following of this description be denoted as force/pressure sensor or only sensor.  
         [0027]    A system  20  for measuring flatness of a strip  1  of rolled material comprises a measuring roll  2 , which has a number of force/pressure sensors  22  that are situated in a certain pattern on said roll. Each sensor  22  generates an measurement output signal U pi  depending on the pressure of the flat sheet on to the sensor and a Wrap Angleα of the strip on the measuring roll  2 . Said system  20  also comprises a Flatness Determination Unit  30 , which is arranged for calculating a value corresponding the wrap angle α based on said measurement output signals U pi  and, based thereon, the flatness of the strip.  
         [0028]    A flatness determination signal may be derived from at least one measurement signal U pi . As mentioned herein above, each separate measurement signal U pi  is generated by a corresponding measuring device of all measuring devices belonging to at least one of all measurement zones of a measuring roll and comprises one or more measurable values for calculating at least one of following quantities or vectors: strip tension vector T, wrap angel , distributed force vector F 2 , force vector F mi , flatness vector Δσ 1  [N/mm 2 ] and/or a corresponding quantity flatness vector Δσ 2  [I-unit]. The flatness determination signal is an input signal to a flatness determination unit for calculating at least one of said quantities or vectors. The flatness determination signal comprises a force component signal (U Fi ) and said force component signal (U Fi ) includes a train of electrical pulses.  
         [0029]    A flatness determination signal may be derived by a number of said separate measurement signals U pi . Each of said measurement signals includes a train of electrical pulses, which are synchronized and combined to aflatness determination signal for calculating at least one of said quantities or vectors. Different known techniques for combining such signals are possible, for example integration, signal addition, signal subtraction, etc.  
         [0030]    The generated signals U pi  or the derived flatness determination signals are input signals to the Flatness Determination Unit  30  for calculating the quantities Wrap Angle α, the force vector Fm i  for the corresponding measurement zone, Strip Tension T and Distributed Force F 2  on each sensor/transducer, which quantities are used for calculating the flatness  1  and  2  corresponding to relative strain in I-unit by means of the Flatness Determination Unit  30 . No tensiometer measurement load cells located elsewhere, e.g. fixed at the shaft bearings of a measuring roll shaft, are needed for determining the strip force on the measuring roll in the new invented system and all the above listed quantities are provided as output values.  
         [0031]    The generated signals U pi  or the derived flatness determination signals could be characterised as a computer data signal. The signals may be superimposed on a carrier waves for transmission of the signal values and characteristics from the sensors to a signal processing unit for separating and determining said signal values and characteristics, e.g. a value for calculating a flatness vector according to any of Δσ 1 , Δσ 2 .  
         [0032]    In the following the Flatness Determination Unit, FDU, of a system  50  according to the invention will be described with reference to FIG. 5. As long as each zone and corresponding output signals are treated separately and no mixing or integration over the zones is performed by the system all measurement zones, channels and signal paths of the system are parallel and designed exactly in the same way. Therefore, in the following only one signal path of the measurement system will be described.  
         [0033]    Every time a sensor is influenced by the strip passing a voltage or/and current is generated. The input signal to the sensor has a frequency f c . When a force is applied to the measuring roll the input signal becomes a carrier wave that is modulated in proportion to the applied force. The signal may be sampled before it is transmitted to the FDU.  
         [0034]    Each sensor having no contact with the strip will generate a noise signal. The FDU has synchronising circuits that generate synchronise pulses indicating the beginning and the end of a time period, called a time slot, during which the contribution from sensors that are in contact with the strip will be integrated. During the time interval when the sensors have no contact with the strip the noise signals will be neglected. The clock circuits also generate clock pulses for synchronisation of the different blocks and processes of the system.  
         [0035]    Measurement signals, analogue or digital, will be transmitted from the measurement zones of the measuring roll  52  via the channels  54  to the FDU  56 . The FDU  56  will have one input port and one signal treatment device  58  for each channel  54 . In this embodiment, the force signal is Amplitude Modulated (AM) on a carrier wave having the carrier frequency f c . However, a person skilled in the art can chose and apply any transmission method, such as any other modulation method or a method wherein no modulation is done.  
         [0036]    One of the tasks of the signal treatment device  58  is to demodulate the input signal. Other signal operations carried out by the signal treatment device  58  are filtering and rectifying.  
         [0037]    By multiplying an AM input signal with a rectification signal the input signal will be demodulated. After demodulation, the signal comprises both the force signal component U Fi , a DC component and the carrier wave. The only useful signal is the force signal component U Fi . A connected standard filter will remove the DC component. The signal treatment is finished and the force signal component U Fi  is forwarded to the signal processing unit  60  or, shorter, signal processor, of the FDU  50 .  
         [0038]    The method and signal processing unit  60  for determining different quantities out of the signal treated force signal component U Fi  will now be described in more detail.  
         [0039]    The output of the signal treatment device  58  is a force signal component U F  consisting of force pulses. Each pulse of the force signal component contains information about the force and wrap angle. The amplitude Â of each pulse is dependant on the force against the signal generating sensor  22  and the length of each pulse is dependent on the wrap angle α and the strip velocity. The wrap angle α determines the length of the strip contact area against the measuring roll and the velocity determines the time for a sensor to pass that area.  
         [0040]    The first step  151  is to extract and determine the force vector Fm i  for the corresponding measurement zone i, i=1,2,3, . . . ,n and the wrap angle α. This step,  151 , is accomplished by a quantity processor block  62 . The quantities Fm i  and α are forwarded in digital form as signals to a tension processor block  64  that, in step  152 , calculates the tension T [N] over the strip by generating the sum of force vectors Fm i  for all measuring zones. Said sum is divided by the Sinus value of the wrap angle α, in accordance with the formula  
           T=Σ Fm   i /(2Sin α/2)  
         [0041]    The quantities T, α and Fm i  are forwarded in digital form as signals to separate output ports  266 ,  268  and  270  for further purposes in the rolling mill system, e.g. display. T is also transmitted to a Flatness Processor  74  that will be described further down in this description. The force vector Fm i  is forwarded to an edge compensator  68  in the next step  153 . Said device/block  68  introduces the width w of the strip and if necessary, the strip position on the measuring roll. The width of the strip varies and for determining the correct flatness value and tension and force distributions, the width variation must be considered. The result of the this calculation is the force distribution vector F 2  [N/mm]. The digital signal representing the quantity F 2  is transmitted to an average generator block  70 , a Relative Force Processor  72  and an output port  272 , In the following two steps,  154  and  155 , an average distribution force F 2av  is generated by means of the average generator block  70  and then, the second step  156 , calculate the scalar factor  
           F   R =( F   2   −F   2av )/F 2av    
         [0042]    by means of a Relative Force Processor  72 . The flatness vector Δσ 1  [N/mm 2 ] is then calculated by use of a flatness vector generator block  74  in the following step  156 . The thickness vector t is used in this step  156  as an input to the generator  74 . The flatness vector Δσ 1  is calculated by use of the formula  
         Δσ 1   =F   R    T /( w t )  
         [0043]    One further step  157  may be taken—that is to transform the flatness vector Δσ 1  [N/mm 2 ] to a corresponding dimensionless quantity flatness vectorΔσ 2  [I-unit]. The flatness vector Δσ 1  [N/mm 2 ] is forwarded to a E-module processor block/step  76 / 157  and the flatness vectorΔσ 2  is generated as an output  280 . By dividing the flatness vector Δσ 1  [N/mm 2 ] with the modulus of elasticity E, the corresponding dimensionless flatness vectorΔσ 2  is generated. The FDU  56  has a flatness vectorΔσ 1  output  274 . The quantities Δσ 1  and Δσ 2  are forwarded in digital form as signals to said output ports  274  and  276  for further purposes in the rolling mill system, e.g. control and display purposes.  
         [0044]    The method is repeated each time as new measured information from the measuring devices is received by the Flatness Distribution Unit.  
         [0045]    The steps, blocks and the devices discussed in the embodiment according to FIG. 5 may be implemented as hardware circuits or as software routines in a processor or central processing unit, CPU. Therefore, the invention is implemented as a computer program product containing computer program code elements or software routines that when run on a computer or processor will carry out the steps of a method according to any of claims 9-14.  
         [0046]    The present invention is not limited to the above-described preferred embodiments. Various alternatives, modifications and equivalents may be used. Therefore, the above embodiments should not be taken as limiting the scope of the invention, which is defined by the appended claims.