CONTROL DEVICE FOR SUCCESSIVE ROLLING MILL

Abstract: A rolling mill control device detects a dimension or dimensions of a product material between two mill stands (3, 4), and forecasts a width variation value of the material at a downstream stand on the basis of rolling characteristics of the material, etc. The position of an upstream stand is then varied to reduce the forecast value to zero. Feedback control is also effected on the position of the upstream stand based upon the difference between a reference width and an actually measured value.

Description: This invention relates to a successive VH-type rolling mill comprising: an i-th stand arranged to reduce rolling material in the direction of a first transverse dimension; an (i-1)-th stand upstreasm of said i-th stand and arranged to reduce said rolling material in the direction of a second transverse dimension; width measuring means for determining a value (bi) representing said second transverse dimension of rolling material at the delivery side of said i-th stand ; control means arranged for controlling a roll separation device at said (i-1)-th stand to reduce the difference between a measured value and a value representing a reference dimension; dimension determining means for determining dimension values (hi-1) representing at least said second transverse dimension of rolling material betweensaid (i-1)-th stand and said i-th stard; forecasting means for supplying in response to said dimension values determined by said determining means and in accordance with a coefficient obtained from the characteristics of said rolling mill and the properties of said rolling material, a forecast value representing a variatior in transverse dimensions of said rolling material at the delivery side of the i-th stand located downstream of said determining means, which variation represents a deviation of at least said second transverse dimension from a reference dimension; and means in said control means to control the roll separation device at said (i-1)-th stand to reduce the forecast value of said forecasting means. Such a device is known from DE-A-1 918 449. Further relevant devices are shown by DE-A-16 02 168 and US-E-27 370. The invention is applicable inter alia to a steel bar or wire rolling mill in which the dimensions of a rolling material are controlled. One example of the arrangement of a successive rolling mill is shown in Figure 1 of the accompanying drawings. The successive rolling mill comprises i stands. In Figure 1, reference numeral 1 designates a #1 mill stand; 2, a #2 stand; 3, a #i-1 stand; 4, a #i stand; and 5, the rolling material. The succesive rolling mill in Figure 1 is a so-called VH type rolling mill. That is, horizontal rolling machines (the odd-numbered stands in Figure 1) and vertical rolling machines (the even-numbered stands in Fig. 1) are alternately arranged. For instance, the #i-1 stand rolling machine 3 is a vertical rolling machine which carries out rolling in the direction X. In fig. 1, reference character bi-l designates the lateral width of the rolled material at the output of the #i-1 rolling machine, and reference character hi-l designates the height thereof. The #i rolling machine is a horizontal rolling machine which carries out rolling in the direction Y. Reference character bi designates the lateral width at the output thereof, and reference character hi designates the height. In a conventional successive rolling mill such as a bar or wire rolling mill, in order to reduce tension of the material between the stands to zero, loop control or a tension control mechanism has been employed. However, a successive rolling mill in which the dimensions of the rolling material are dynamically controlled has yet to be provided in the art because of the following reasons: (1) the tolerances on the dimensions of the products have not been severe, and (2) elongation of the material due to a variation in the load during rolling is small. (This reduces the effect of transmitting a variation of a rolling material at the input side to the delivery side, and therefore the accuracy of product dimension is not greatly varied.) Thus, the conventional control is disadvantageous in that the dimensional accuracy is low, because, for example, the dimensional variation resulting from variations in the temperature of the rolling material is not controlled at all. Although it is known from DE-A-16 02 168 and US-E-27 370 to control the i-th stand in accordance with dimensional information from the delivery side of the i-th stand, such a system provides insufficient dimensional accuracy. An object of the invention is to improve the dimensional accuracy produced by a control device according to the first paragraph of this specification. According to the invention, the control device initially defined is characterised in that said measuring means at the delivery side of said i-th stand is connected to supply said measured value to said control means, whereby said control means is operable to control said (i-1)-th stand in dependence upon the transverse dimension (bi) of the material, measured at the delivery side of said i-th stand, in the direction of said second transverse dimension. Preferred embodiments of the invention are recited in claims 2 to 7. The width of the rolling material at the delivery side of the i-th stand is actually determined, and the roll separation position of the (i-1)-th stand is controlled so that the deviation between the width determined and a reference width at the delivery side of the i-th stand may be reduced substantially to zero, whereby the dimensional accuracy in successive rolling is improved. The use of the forecasting means ensures adequate response speed. The invention is described in detail below with reference to drawings which illustrate preferred embodiments, in which: Figure 1 is an explanatory diagram showing one example of the arrangement of a successive rolling mill; Figure 2 is a block diagram showing a dimension control device according to one embodiment of this invention; and Figures 3a and 3b are characteristic diagrams indicating the relations between the height and width of a rolling material and the depression position of a rolling machine. In Figure 2, reference numeral 3 designates a #i-1 stand; 4, a#i stand; and 5, a rolling material. Screw depression motors 7 and 8 are provided as roll separation devices for the stands, and load cells 9 and 10 detect rolling loads. Screw or depression position detecting pulse oscillators 11 and 12 are coupled to the motors 7 and 8, and motor driving thyristor devices 13 and 14 supply electric power to the motors 7 and 8. At 15 and 16 are shown mill spring control devices for the stands. A motor 20 is provided for driving the rolling roll of the #i-1 stand, and a motor 21 is disposed for driving the rolling roll of the #i stand. Thyristor devices 22, 23 drive respective motors 20 and 21. A loop control device 24 maintains a given amount of loop between the #i-1 stand and the #i stand, and a width measuring device 25 is arranged for measuring the width of the material at the delivery side of the #i stand. A gain controller 26 multiplies a difference Δbi (which is a deviation between the width bi measured by the width measuring device 25 and a reference width bi(REF)) by a predetermined control gain; and the output of the gain controller 26 is fed to a screw position controller 27, which is a PI(D) controller, and by this controller a screw position correction signal is fed to the screw down motor 7 of the #i-1 stand. Further in Figure 2, reference numeral 28 designates a width measuring device for measuring the width of the rolling material at the delivery side of the #i-1 rolling machine; and a height measuring device 29 measures the height of the same. In a divider 30, the difference between a measured value bi-1 of the width measuring device 28 and a reference width bi-1(REF) in the #i-1 stand is divided by the reference width bi-1(REF), and in a divider 31, the difference between a measured value hi-1 of the height measuring device 29 and a reference height hi-1(REF) for the #i-1 stand is divided by the reference height hi-1 (REF). A forecasting device 32 receives the output of the divider 30, for forecasting the change which will be caused in the width at the delivery side of the #i stand 4 by a change in the width at the delivery side of the #i-1 stand 3. Simultaneously, a forecasting device 33 receives the output of the divider 31, for forecasting a change which will be caused in the width at the delivery side of the #i stand 4 by a change in the height at the delivery side of the #i-1 stand. In a gain controller 34, the composite output of the forecasting devices 32 and 33 is multiplied by a predetermined control gain; and in a screw position controller 35, which is a PI(D) controller, and by this controller a screw position correction signal is fod to the screw down motor 7 of the #i-1 stand. In most conventional systems, the loop control device 24 controls the speed of the motor 20 of the i-1 stand whose set speed was Ni-1 (REF), so that the amount of loop between the #i-1 stand 3 and the #i stand 4 is made constant. However, according to this system mentioned above, the dimensions of the products are solely determined by the characteristics of the rolling machine, and therefore it is impossible to dynamically control the dimensions. A mill spring control method (BISRA control) is known in the art, in which, with the aid of the loads detected by the load cells 9 and 10, the mill spring controllers 15 and 16 detect variations in height, to control the screw positions. However, as it is impossible for the method to control dimensions in both directions (i.e. both width and height), the overall dimensions are poor in accuracy. The operation of the control device according to the invention will now be described. The width bi-1 and height hi-1 of the rolling material 5 are measured by the width measuring device 28 and the height measuring device 29 arranged on the delivery side of the #i-1 rolling machine 3. The difference Δhi-1 between the height hi-1 thus measured and the reference height hi-1(REF) of the #i-1 stand is fed to the divider 31. Similarly, the difference between the measured width bi-1 and the reference width bi-1 (REF) is fed to the divider 30. Using the height deviation hi-1 and width deviation Δbi-1 determined at the delivery side of the #i-1 stand, the width deviation Δbi at the delivery side of the #i stand 4 is calculated, to eliminate width deviation Δbi at the delivery side of the #i stand by feedback control. In order to eliminate the width deviation at the delivery side of the i-th machine 4, it is necessary to control the position of the stand 3, as described in detail below. Figure 3a indicates height (hi) deviations and width (bi) deviations caused when the screw position Si of the #i stand rolling machine is varied. Figure 3b indicates height (hi-1) and width (bi-1) deviations, and also height (hi) and width (bi) deviations at the delivory side of the respective i-1th and i-th rolling machines caused when the screw position Si-1 of the #i-1 stand rolling machine is varied. A method of correcting the position Si of the #i rolling machine 4 and that Si-1 of the i-1 rolling machine 3 are available in controlling the width bi at the delivery side of the #i stand rolling machine, as is apparent from Figures 3a and 3b. When the screw position Si of the #i stand rolling machine is corrected, not only the width bi, but also the height hi is changed. On the other hand, when the screw position Si-1 of the #i-1 stand rolling machine 3 is corrected, the height hi at the delivery side of the i-th stand is scarcely changed. Based on this fact, the width deviation Δbi at the delivery side of the #i stand is compensated by controlling the screw position of the #i-1 stand rolling machine 3. More specifically, the width deviation Δbi-1 and height deviation Δhi-1 at the delivery side of the #i-1 stand rolling machine 3 are applied to the dividers 30 and 31, respectively, where they are divided by the reference width bi-1(REF) and reference height hi-1(REF) at the delivery side of the #i-1 stand. The output (hi-1(REF)-hi-1/hi-1 (REF)) of the divider 31 represents a height deviation factor at the delivery side of the #i-1 rolling machine 3, and the output (bi-1(REF)-bi-1/bi-1 (REF)) of the divider 30 represents a width deviation factor at the delivery side of the #i-1 stand. The output of the divider 30 is applied to the forecasting device 32, while the output of the divider 31 is applied to the forecasting device 33. The forecasting device 32 forecasts the width deviation at the delivery side of the #i stand using a coefficient representing the influence that the width deviation factor at the delivery side of the #i-1 stand rolling machine 3 has on the width deviation at the delivery side of the #i rolling machine. On the other hand, the forecasting device 33 forecasts the width deviation at the delivery side of the #i stand 4 using a coefficient representing the influence that the height deviation factor at the delivery side of the #i-1 stand rolling machine 3 has on the width deviation at the delivery side of the #i stand. The outputs of the forecasting devices 32 and 33 take values which are determined from the characteristics of the rolling machines and the properties of the rolling material, and which can be calculated in advance. Accordingly, by combining the outputs of the forecasting devices 32 and 33, the width deviation Δbi* at the delivery side of the #i stand due to the height and width deviations at the delivery side of the #i-1 rolling machine 3 can be obtained. The forecast deviation Δbi* is applied to the gain controller 34. In the gain controller 34, in order to eliminate or reduce the forecast width deviation Δbi*, the composite output is multiplied by a predetermined gain for correcting the position of the #i-1 stand 3, to provide an output. The value of the gain control multiplier of the gain controller 34 can be calculated from the gradient of the bi deviation characteristic curve with Si-1 changed, in Figure 3b. The output of the gain controller 34 is applied to the screw position controller 35. In the controller 35, the output of the gain controller 34 is subjected to PI(D) control, and a position correction signal is applied to the screw down device including the screw down motor 7, the pulse oscillator 11 and the motor driving thyristor device 13. The motor 7 is driven by the motor driving thyristor device 11 until the screw position detected by the pulse oscillator 11 coincides with the screw position correction signal. By this control, the width deviation at the delivery side of the #i stand due to a deviation in the dimension of the material at the delivery side of the #i-1 stand is compensated. In the above-described system, the dimensions of the material at the delivery side of the #i-1 stand are measured to control the dimensions of the material at the delivery side of the #i stand, and therefore the control is excellent in response; however, the dimensional accuracy is not always sufficient. Therefore, in order to obtain even more satisfactory dimensional accuracy, the width measuring device 25 is provided at the delivery side of the #i stand rolling machine 4, so that the feedback control is carried out with actually measured values. That is, the width is measured by the width measuring device 25 provided at the delivery side of the #i stand rolling machine 4, and the difference Δbi between the width thus measured and the reference width bi(REF) at the delivery side of the #i stand is applied to a gain controller 26. The gain controller 26 is similar in arrangement to the gain controller 34. The output of the gain controller 26 is supplied to a screw position control device, where the output of the gain controller 26 is subjected to PI(D) control, and similarly as in the case of the screw position control device 35, a screw position correction signal is applied to the screw down device of the #i-1 stand. In the above-described embodiment, the height measuring device 29 actually measures the dimension of the rolling material 5 at the delivery side of the #i-1 stand; however, the dimension may be determined by other means, i.e. by calculating from the screw position Si-1 of the #i-1 stand, the mill spring constant and the rolling load. Furthermore in the above-described embodiment, the height and width of the material at the delivery side of the #i-1 stand are determined, so that the width deviation of the material at the delivery side of the #i stand can be forecast from the percentages of deviation in the height and width thus determined. However, the width deviation of the material may be forecast by determining only one of the height and width. Moreover, the forecast may be achieved by determining the height and width of the material at a point upstream of the #i-1 stand instead of the delivery side of the #i-1 stand. As is apparent from the above description, according to the invention, the deviation in one or more transverse dimension of the material between any two stands is utilized to forecast the width deviation of the material at the delivery side of the #i stand located downstream, and the screw position of the #i-1 stand rolling machine is controlled so that the width deviation thus forecast is reduced to zero; and the width of the material at the delivery side of the #i stand rolling machine is actually measured, and the screw position of the #i-1 stand is controlled so that the difference between the width thus measured and the reference width of the material at the delivery side of the stand is reduced to zero. Therefore, the controller of the invention is excellent in response and can perform rolling control with high accuracy.

Claims: 1. A successive VH-type rolling mill comprising: an i-th stand (4) arranged to reduce rolling material (5) in the direction of a first transverse dimension; an (i-1)-th stand (3) upstream of said i-th stand and arranged to reduce said rolling material (5) in the direction of a second transverse dimension; width measuring means (25) for determining a width value (bi) representing said second transverse dimension of rolling material (5) at the delivery side of said i-th stand (4); control means (26,27) arranged for controlling a roll separation device at said (i-1)-th stand (3) to reduce the difference between a measured value and a value representing a reference dimension; dimension determining means (28,29) for determining dimension values (hi-1) representing at least said second transverse dimension of rolling material between said (i-1)-th stand (3) and said i-th stand (4); forecasting means (32,33) for supplying in response to said dimension values determined by said determining means and in accordance with a coefficient obtained from the characteristics of said rolling mill and the properties of said rolling material, a forecast value representing a variation in transverse dimensions of said rolling material at the delivery side of the i-th stand located downstream of said determining means, which variation represents a deviation of at least said second transverse dimension from a reference dimension; and means (34,35) in said control means to control the roll separation device at said (i-1)-th stand to reduce the forecast value of said forecasting means (32,33), characterized in that said measuring means (25) at the delivery side of said i-th stand (4) is connected to supply said measured value to said control means (26,27), whereby said control means (26,27) is operable to control said (i-1)-th stand in dependence upon the transverse dimension (bi) of the material measured, at the delivery side of said i-th stand, in the direction of said second transverse dimension. 2. A rolling mill as claimed in claim 1 characterised by said dimension determining means comprising width and height detectors (28, 29) arranged proximate said rolling material (5). 3. A rolling mill as claimed in claim 2 characterised by said forecasting means calculating a forecast value on the basis of at least one of said measured dimensions. 4. A rolling mill as claimed in claim 3 characterised by including means for generating height and width deviation values, and dividers (30, 31) for dividing said values. 5. A rolling mill as claimed in claim 4 characterised by said forecasting means comprising a first forecasting device (33) and a second forecasting device (32) respectively forecasting height and width deviations at an output of said i-th stand based on said divided height and width deviation values. 6. A rolling mill as claimed in claim 5 characterised by including means for combining outputs of said first and second forecasting devices, and gain control means (34) receiving said combined output, and outputting a signal for controlling said roll separation device. 7. A rolling mill as claimed in claim 6 characterised by including gain control means (26) receiving a difference between an output of said width detecting means (25) downstream of said i-th stand and a reference value, and outputting a further signal for controlling said roll separation device.

Inventors: ISHIMURA, KOICHI MITSUBISHI DENKI K.K., NIINO, SHUHEI MITSUBISHI DENKI K.K., OHBA, KOICHI MITSUBISHI DENKI K.K., OKAMOTO, KEN MITSUBISHI DENKI K.K.
Applicants: MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1982
Main classification: B21B1
IPC codes: B21B37, B21B1