Abstract:
Method and device for the reduction and/or compensation of speed drops when threading rolled stock into a roll stand whose rolling speed is controlled with a controller, the controller outputting a predefined supplementary value independently of its input in a predefined transition time interval shortly before, during, or shortly after the rolled sock is threaded into the roll stand.

Description:
This application is a 35 USC 371 of PCT /DE98/01587 field Jun. 9, 1998. 
     FIELD OF THE INVENTION 
     The present invention relates to a method and a device for the reduction and/or compensation of speed drops when threading rolled stock into a roll stand whose rolling speed is controlled using a controller. 
     BACKGROUND INFORMATION 
     In a production line, the incoming strip stock causes an abrupt load In each stand on the first pass. For the roll drive, this signifies a steep increase of the moment of load. Due to the finite moment of inertia of the drive, made up of the moments of inertia of the motor, the couplings, spindles, gears and rollers, the speed of the drive drops initially. Thereafter, the speed controller brings the speed back to its setpoint. The drop in speed causes a deceleration of the incoming strip as compared to the setpoint speed predetermined in the schedule of passes, resulting in a backward slip of the material. This backward slip is expressed in the formation of a kink in the strip downstream from the stand. This kink may only be of such a magnitude that it can be controlled by the kink control and the kink lifter. The precision of the run-out thickness of the strip is also influenced. 
     In the case of high demands on the magnitude of the kink, primarily with short load increase times such as occur on the last stands of a production line, a standard PI speed controller is frequently not sufficiently dynamic. 
     SUMMARY PRESENT 
     An, object of the present invention is to provide a method and a device for the reduction and/or compensation of speed drops when threading rolled stock into a roll stand. 
     The objective is attained according to the present invention by a method and a device which considerably reduce speed drops as shown, for. example, in FIG.  3 . 
     The method according to the present invention is used to particular advantage for I controllers or partial subgroup controllers designed as I controllers. 
     It is of particular advantage to use the method according to the present invention for a speed controller. If speed control is supplemented by a load monitor, integrators being used to model the path dynamics, then the method according to the present invention is also used advantageously for the integrators or a portion of the integrators for modeling the path dynamics in the load monitor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows an exemplary embodiment of a control which is connected according to the present invention. 
     FIG. 2 shows the result of a convational method for the reduction of speed drops; 
     FIG. 3 shows the result when the method according to the present invention is used to reduce speed drops. 
     FIG. 4 shows an exemplary embodiment of a control and precontrol which are connected according to the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows a block diagram of a controller according to the present invention. The roll stand is driven via a motor  2  controlled big a power circuit, a moment of load M L  acting against the motor torque. In this connection, the roll speed is the integral of the difference of the drive torque and moment of load. This physical relationship is modeled by integrator  3 . This controlled system is controlled in the exemplary embodiment by a PI controller  1  as a function of the difference of desired speed n* and actual speed n. In one embodiment according to the invention, when rolled stock, particularly a rolled strip, is threaded into the roll stand, a supplementary value W Z  for a specified transition time interval Δt is output by the I component of the PI controller independently of its input. 
     In order to reduce the speed drop, a load monitor  16  is provided in the exemplary embodiment. It has a feedback integrator  6 , a proportional element  8  and a load integrator  4 . At summing point  7 , speed R simulated by integrator  6 ) is compared with the measured speed n of the motor. The difference, among other things, is supplied to load integrator  4 . In the steady-state condition, its output M L  corresponds to the steady-state moment of load M L . In summing unit  9 , the latter is compared with the measured motor torque (motor current x flux) and the difference is supplied to integrator  6 . The simulated moment of load M L  is added to the spend controller output when switch  10  is closed. The speed controller can then be operated as a P controller. 
     For further improvement, the method according to the present invention can be used for load monitor  16 , for load integrator  4  in particular. 
     Rolling force signal  14  in FIG. 1 servos as a trigger signal for the first pass. when rolling force signal  14  occurs, supplementary value generator  17  outputs a supplementary value W Z  for the duration of transition time interval Δt. This supplementary value W Z  is the input variable into load integrator  4  and/or, if a load monitor  16  is used, in the I component of PI controller  1 . If supplementary value W Z  is present, the load integrator  4  (i.e., the I component of PI controller  1 ) outputs supplementary value W Z  independently of its input. Advantageously, supplementary value W Z  amounts to twice the expected moment of load M L . In a further development, (with switch  11  closed), supplementary value W Z  may also be supplied only to the integral component (I component) of the PI controller. Switch  10  of the output of load monitor  16  is then open or no load monitor is provided. 
     Supplementary value W Z  may be a time-dependent value or, advantageously, a constant value. Advantageously, this value amounts to 1.5 to 2.5 times, 2 times in particular, the expected moment of load when the rolled stock is threaded into the roll staid. The transition time interval is advantageously 10 msec to 100 msec, in particular, 20 msec to 40 msec long. 
     As a supplement to the method according to the present invention, a speed correction unit  18  can be used which outputs a correction setpoint value Δn* as described in, for example, Japanese Patent Application Nos. 833911, 7245975 and 6284763. Already before the first pass, the correction setpoint value Δn*, which is a function Co the absolute value of the moment of load to be expected, is added to the desired speed setpoint value n N *, resulting in an actual setpoint speed n*. At the time of the first pass, i.e., threading time t e , which is also detected via rolling force signal  14 , correction setpoint value Δn* is canceled according to a suitable time function. 
     Accordingly, as shown in FIG. 4 (element  18 ) the rolled stock may be threaded into the roll stand with the setpoint speed (n*) of the rollers of the roll stand being increased by a predefined value (Δn*) and thereafter reduced to a desired setpoint speed (N n *) after threading-in the rolled stock. Moreover, it is contemplated that the setpoint speed (n*) is reduced or lowered according to a hyperbole. 
     FIG. 2 shows the variation of the speed of rolling over time t during threading of a rolled strip. The rolled strip is threaded in at time 0.5. Reference symbol  20  identifies the desired setpoint speed. Reference symbol  21  identifies the speed drop with simple speed control without additional measures. Reference symbol  22  shows by way of example the speed variation when a known correction setpoint transmitter as is identified in FIG. 1 with reference symbol  18  is used. 
     FIG. 3 shows the speed variation in the method according to the present invention. The rolled strip is threaded in at time 0.5. Reference symbol  23  identifies the desired setpoint speed. Reference symbol  25  identifies the speed drop with simple speed control without additional measures. Reference symbol  24  identifies the speed of rolling when the method according to the invention is used with a load monitor corresponding to reference symbol  16  in FIG.  1 . 
     FIG. 4 shows an exemplary embodiment of the present invention according to FIG. 1 having an additional precontrol. The precontrol has a PI element  30  and an I element  31 . At the output of PI element  30 , which is embodied as controller  1 , a moment setpoint value M v * is picked off. At the output of I element  31 , setpoint speed value n n * is generated according to the corresponding setpoint value in FIG.  1 . The input variable into the precontrol is a speed setpoint value n v *. Via an optional switch  32 , supplementary value W z  is also supplied to PI element  30  in the precontrol.