CONTROL DEVICE FOR A CONTINUOUS ROLLING MACHINE

Abstract: A control device for a continuous rolling machine effects feedback control by measuring vertical and lateral dimen­ sions at a point after an ith mill stand, and by controlling the tension in the material between an i-1th and the ith mill stand and the position of the ith mill stand to reduce the differences between the detected dimensions and reference dimensions to zero. A shape correction device may be used which calculates lateral and vertical dimension change values for the i-1th stand, which are used to control the position of the i-1th stand and the tension in the material between an i-2th mill stand and the i-1th stand to assist in bringing the actual dimensional output values into coincidence with the refer­ ence values.

Description: This invention relates to a multi-stage continuous rolling machine system comprised of successive mill stands having roll axes oriented substantially perpendicularly to each other and a control system comprising: a lateral dimension detector for measuring a lateral dimension of material at the exit of an ith mill stand; means for determining a lateral deviation as the difference between said lateral dimension and a reference lateral dimension; first tension control means for controlling the tension between first and second mill stands for control of said lateral dimension and depression control means for controlling the depression position of said first mill stand. Such a system is disclosed in US-A-3 650 135. Further related systems are known from US-A-3 841 124, US-A-3 526 113 and GB-A-1 256 067. A continuous rolling machine controlled by the system may have a profiled roll and may be, for example, a bar steel mill or a wire mill. An example of the configuration of a continuous rolling machine of this type is shown in Fig. 1, of the accompanying drawings. Fig. 1 shows a continuous rolling machine comprising i mill stands, wherein are illustrated a #1 mill stand 1, a #2 mill stand 2, an #i-1 mill stand 3, and #i mill stand 4, and a rolling material 5. Fig. 1 illustrates a so-called VH type rolling machine, wherein horizontal mill stands (odd numbered stands in Fig. 1) and vertical mill stands (even numbered stands in Fig. 1) are alternately arranged. In this specification the term "vertical dimension" means the dimension of the rolled material determined by the spacing of a set of rollers irrespective of their orientation in space. The term "lateral dimension" means a dimension perpendicular to the "vertical dimension". For instance, the #i-1 mill stand 3 is a vertical mill performing rolling in the X direction wherein bi-1 represents the lateral dimension and hi-1 represents the vertical dimension at the exit of the #i-1 mill stand 3. On the other hand, the #i mill stand 4 is a horizontal mill performing rolling in the Y direction, wherein bi represents the lateral dimension and hi represents the vertical dimension at the exit of the #i mill stand 4. Some conventional continuous rolling machines such as bar steel and wire mills employ a non-tension control method (AMTC) for reducing the tension between the mill stands to zero. Although the prior art indicated above discusses the relationship between stock tension and dimensional control, there is no indication or suggestion that dimensional accuracy may be improved by extending a control, based on current downstream dimensions, of tension and screw position at an upstream mill-stand further to anticipate the input requirements determined by the control settings of a downstream mill-stand. In particular, although US-A-3 526 113 relates to V-H rolling and recognises the influence of inter-stand tension on dimensional stability, the disclosed configuration using loop control between stands is directed at excluding any disturbing influence from variations in inter-stand tension, by endeavouring to maintain such tension constant by ensuring consistent loop conditions. Therefore, the document leads specifically away from employing inter-stand tension as an active control variable in a multi-stand configuration. An object of the invention is to provide a V-H multi-stage continuous rolling machine system having a control system capable of providing improved and enhanced dimensional accuracy of the rolled product. According to the invention, the multi-stage continuous rolling machine system initially defined is characterized in that: said first mill stand is an (i-1)th mill stand and said second mill stand is said ith mill stand; in that shape correction means is provided to receive the output of said tension control means and a signal representing said lateral deviation (Δ bi) and is arranged to compute in dependence thereon a change value (Δ hi-1*) in vertical dimension at said (i-l)th stand and a change value (Δ bi-1*) in lateral dimension at said (i-l)th stand as will reduce said lateral deviation (Δ bi) to zero in accordance with a predetermined algorithm; in that said depression control means is arranged to control the depression position of the (i-l)th stand in accordance with said change value (Δ hi-l*) in the vertical dimension as calculated by said shape correction means, and in that second tension control means is provided for controlling the tension between an (i-2)th mill stand and the (i-l)th mill stand in accordance with said change value (Δ bi-1*) in the lateral dimension as calculated by said shape correction means. In some embodiments, said first tension control means is connected to receive said deviation and is arranged to control the tension between said ith and (i-1)th mill stands to tend to reduce said deviation to zero. Preferably, vertical dimensions detecting means is provided for measuring a vertical dimension of material at the exit of said ith mill stand and wherein said shape controlling means is connected to receive a signal representing a vertical deviation as the difference between said vertical dimension and a reference vertical dimension and is arranged to provide said change values in dependence thereon. Expediently, further depression control means are connected to receive a signal representing said vertical deviation and are arranged to supply a depression position control signal for control of the depression position of said ith mill stand, to tend to reduce said vertical deviation to zero. Said first tension control means may be connected to receive said depression position control signal and is arranged to control said tension in dependence thereon. Expediently, said shape correction means is connected to receive said depression position control signal and is arranged to provide said change values in dependence thereon. The invention is described in detail below with reference to drawings which illustrate preferred embodiments, in which: Fig. 1 is a schematic view for one example of a conventional continuous rolling mill; Fig. 2 is a block diagram showing a dimension control device of a continuous rolling mill according to one embodiment of this invention; Figs. 3(a) and 3(b) are characteristic diagrams showing the relationships between the rolling position and the speed of the rolling mill and the vertical and lateral dimensions; Fig. 4 is a block diagram of a second embodiment of the invention; and Fig. 5 is a block diagram of a further embodiment of the invention. In Fig. 2 there are shown an i-1th mill stand 3, an ith mill stand 4, a rolling material 5 and rolling drive motors 7, 8 for the respective mill stands. Load cells 9, 10 are mounted on respective mill stands for the detection of rolling loads, and pulse generators 11, 12 are connected to the rolling drive motors 7, 8, respectively, for the detection of screw or depression positions (roller clearance). Motor driving thyristors 13, 14 are provided for supplying electric power to the rolling drive motors 7, 8; mill rigidity control devices 15, 16 are provided for respective mill stands, and drive motors 21, 22 are arranged for the rolling rolls of the i-1th mill stand 3 and the ith mill stand 4. Driving thyristors 23, 24 are provided for the respective motors 21, 22, and speed detectors 25, 26 are disposed for speed detection of the drive motors. A vertical dimension detector 31 for the detection of the vertical dimension of the material at the exit of the ith mill stand 4 and a lateral dimension detector 32 for the detection of the lateral dimension of the material are arranged at the exit of the ith mill stand 4. A deviation Δbi of the lateral dimension bi detected by the lateral dimension detector 32 from a reference lateral dimension biREF is supplied to the speed control device 34 to control the rolling speed of the ith mill stand, and thus the tension between the i-1th and the ith mill stands. Further, a deviation Δhi of the vertical dimension hi detected by the vertical dimension detector 31 from a reference vertical dimension hiREF at the exit of the ith mill stand is supplied to a shape correction device 35. In Figure 2, the shape correction device 35 receives dimensional deviations Δhi, Δbi of the material at the exit of the ith mill stand, and the control output ΔVi from the speed control device 34 and calculates such a change value Δhi-1* in the vertical dimension and a change value Δbi-1* in the lateral dimension of the i-1th mill stand 3 as will reduce the deviation Δbi to zero in accordance with a predetermined algorithm. A rolling or depression control device 36 corrects the rolling position of the i-1th mill stand in accordance with the change value Δhi-1* in the vertical dimension calculated by the shape correction device, and a speed control device 37 corrects the speed of the drive motor 21 driving the i-1th mill stand, and thus the tension between the i-2th and the i-1th mill-stands, in accordance with the change value Δbi-1* in the lateral dimension, as calculated by the shape correction device 35. The control system of this embodiment of the invention will now be explained. The rolling speed of the ith mill stand is controlled in order to control the lateral dimension of the material at the exit of the ith mill stand 4 in this invention and the reason therefor will firstly be described. Fig. 3(a) shows changes in the vertical dimension hi and the lateral dimension bi of the rolling material 5 at the exit of the ith mill stand 4 in the case where the rolling position Si of the ith mill stand 4 is changed, and Fig. 3(b) shows the change in the tension σ between the i-1th mill stand and the ith mill stand as well as changes in the vertical dimension hi and the lateral dimension bi of the rolling material at the exit of the ith mill stand 4 in the case where the speed ΔVR/VR of the ith mill stand 4 is changed. As can been seen from Fig. 3(b), a change in the speed of the ith mill stand 4 causes no substantial change in the vertical dimension hi, with only the lateral dimension bi being changed. Accordingly, in order to change the vertical dimension hi at the exit of the ith mill stand 4, it is necessary to control the screw position Si of the ith mill stand 4. However, control of the rolling position Si for the ith mill stand also causes the lateral dimension bi to be changed and, therefore, the screw position Si cannot be solely controlled. In contrast, as can be seen from Fig. 3(b), if the lateral dimension of the material at the exit of the ith mill stand is controlled by controlling the rolling speed ΔVR/VR of the ith mill stand, this has no substantial effect on the vertical dimension hi. Accordingly, the lateral dimension can be controlled satisfactorily by controlling the speed of the ith mill stand to thereby control the tension between the i-1th mill stand and the ith mill stand. Specifically, the deviation Δbi of the lateral dimension bi detected by the lateral dimension detector 32 disposed at the exit of the ith mill stand 4 from a reference lateral dimension biREF at the exit of the ith mill stand is supplied to the speed control device 34. The speed control device 34 generates such a speed correction signal ΔVi as will reduce the deviation Δbi of the lateral dimension at the exit of the ith mill stand based on the relation shown in Fig. 3(b) to zero, and thereby controls the speed of the motor 22 for driving the ith mill stand 4. That is, the speed correction signal ΔVi generated by the speed control device 34 is inputted, together with a reference speed signal NiREF of the ith mill stand, to the thyristor 24. The thyristor 24 controls the speed of the motor 22 in accordance with the speed signal thus input. Then, speed control is continued until the feedback signal from the speed detector 26 agrees with the speed signal inputted to the thyristor 24. The speed of the ith mill stand is corrected by the speed control device 34 as described above, but, if the correction amount is too great, this may increase the tension (or compressive force) between the i-1th mill stand and the ith mill stand excessively, thereby resulting in the risk of twisting or buckling the rolling material 5. In order to avoid such danger, dimensional deviations Δhi, Δbi of the rolling material at the exit of the ith mill stand and the speed correction amount ΔVi for the ith mill stand are inputted to the shape correction device 35 for the i-1th mill stand and, in order to change the shape of the rolling material at the exit of the i-1th mill stand, a correction for rolling and for the speed are applied to the rolling control device 36 and the speed control device 37 for the i-1th mill stand. The operation of the shape correction device 35 for the i-1th mill stand will be explained. The shape correction device 35 for the i-1th mill stand is provided with dimensional deviations Δhi, Δbi of the rolling material at the exit of the ith mill stand 4 and calculates such a change value Δhi-1* in the vertical dimension and a change value Δbi-1* in the lateral dimension of the rolling material at the exit of the i-1th mill stand as will reduce the dimensional deviations to zero. While various forms of calculation algorithms may be considered depending on the characteristics of the rolling mills, two non-limitative examples are described herein. As one example of the calculation algorithm, a change value Δhi-1* in the vertical dimension and a change value Δbi-1* in the lateral dimension at the exit of the i-1th mill stand are calculated so that the change Δhi in the vertical dimension and the change Δbi in the lateral dimension at the exit of the ith mill stand are reduced to zero: Δbi-1*= ―1 αhi αbi-1 · Δhi Δhi-1*= ―1 αbi αhi-1 · (Δbi- αbi αbi-1 · Δbi-1*) where αhi αbi-1 represents an effect coefficient of the change in the lateral dimension of the rolling material at the exit of the i-1th mill stand relative to the vertical dimension of the rolling material at the exit of the ith mill stand, αbi αhi-1 represents an effect coefficient of the change in the vertical dimension of the rolling material at the exit of the i-1th mill stand relative to the lateral dimension of the rolling material at the exit of the ith mill stand, and αbi αbi-1 represents an effect coefficient of the change in the lateral dimension of the rolling material at the exit of the i-1th mill stand relative to the lateral dimension to the rolling material at the exit of the ith mill stand. As another example of the calculation algorithm, in the case where both of the mill rigidities of the i-1th and ith mill stands are sufficiently high and the change Δhi in the vertical dimension is not so large and thus the rolling change ΔSi is not high, correction for the shape at the exit of the i-1th mill stand is reduced to zero. Δbi is changed by a charige in any one of the dimensions hi-1, bi-1 of the rolling material at the exit of the i-1 th mill stand and the ratio for each of the changes: α=Δhi-1*/Δbi-1* is controlled to a constant value. The change for Δhi-1, Δbi-1 are calculated as below: Δbi= αbi αbi-1 · Δbi-1+ αbi αhi-1 · Δhi-1 where αbi αbi-1 , αbi αhi-1 represent effect coefficients incorporated in equations (1), (2), and Δhi-1*=α · Δbi-1*. By substituting equation (4) into equation (3) with the sign of the instruction value being reversed, Δbi-1* is calculated as: Δbi-1*= ―1 αbi αbi-1 +α · αbi αhi-1 · Δbi The change Δbi-1* is calculated in equation (5) and the change Δhi-1* is calculated in equation (4). If α=0, only Δbi-1* is changed and if α=hi-1/bi-1, the ellipse ratio of the shape at the exit of the i-1th mill stand is made constant. The shape correction device 35 for the i-1th mill stand may be operated such that the device is actuated only when the rolling correction amount ΔSi for the ith mill stand and the speed correction amount ΔVi for the ith mill stand, which are monitored, meet certain limits, or the device may always be actuated irrespective of the values ΔSi, ΔVi. Then, the outputs Δhi-1*, Δbi-1* from the shape correction device 35 for the i-1th mill stand are respectively input to the rolling control device 36 and the speed control device 37 for the i-1th mill stand. The rolling control device 36 for the i-1th mill stand calculates the change in the rolling amount based on Δhi-1* according to equation (6): ΔSi-1= 1 αhi-1 αSi-1 · Δhi-1* where αhi-1/αSi-1 represents an effect coefficient of the change in the rolling amount of the i-1th mill stand relative to the change in the vertical dimension of the rolling material at the exit of the i-1th mill stand. Further, the speed control device 37 for the i-1th mill stand calculates the speed variation ΔVi′ based on Δbi-1* according to equation (7): ΔVi-1′= 1 αbi-1 αVi-1 · Δbi-1 where αbi-1/αVi-1 represents an effective coefficient of the speed variation of the i-1th mill stand relative to the change in the lateral dimension of the rolling material at the exit of the i-1th mill stand. Then, since the lateral dimension at the exit is also changed by the change in the rolling amount, the speed variation ΔVi-1″ resulting from the change in the rolling amount of the i-1th mill stand is calculated according to equation (8): ΔVi-1″= αbi-1 αSi-1 · ΔSi-1 where αbi-1/αSi-1, αbi-1/αVi-1 represent effect coefficients concerning the i-th mill stand, specifically, the change of the screw position and speed change relative to the lateral dimension. Both ΔVi-1′ and ΔVi-1″ are added as a speed variation ΔVi-1 for the i-1th mill stand, by which the speeds for the i-1th and ith mill stands are corrected to thereby change the tension before the i-1th mill stand. In this way, the rolling amount and the speed of the i-1th mill stand are corrected so that the output values of the shape correction device 35 at the exit of the i-1 th mill stand are Δhi-1*, Δbi-1* respectively. While it is necessary to previously determine the effect coefficients ( αhi αbi-1 , αbi αhi-1 , αbi αb-1 , αhi-1 αSi-1 , αbi-1 αVi-1 , αbi-1 αSi-1 for the control of the i-1th mill stand, these can be measured empirically. Further, if there are errors in the coefficients, they do not lead to errors in the final dimension and the shape since the feedback control is applied at the exit of the ith mill stand by the dimension detector. In the above embodiment, although the vertical dimension detector 31 is disposed at the exit of the ith mill stand 4 and the change Δhi in the vertical dimension of the material at the exit of the ith mill stand or the like is inputted to the shape correction device 35 to calculate the change value Δhi-1* in the vertical dimension and the change value Δbi-1* in the lateral dimension at the i-1th mill stand, the vertical dimension detector 31 may be omitted, and the shape correction device 35 can be adapted to calculate Δhi-1* and Δbi-1* based on the change Δbi in the lateral dimension and the control amount ΔVi from the speed control device 34. Further, in the above embodiment, although the speeds of the i-1th and ith mill stands are changed in order to change the tension between the i-2th mill stand and the i-1th mill stand, and the speed for the ith mill stand is changed in order to change the tension between the i-1th mill stand and the ith mill stand, the speed of the i-2th mill stand and the speeds of the i-2th, i-1th mill stands may, alternatively, be changed. Basically, it is required only that the tension between the 1-2th mill stand and the i-1th mill stand, as well as the tension between the i-1th mill stand and the ith mill stand can be controlled. In a second embodiment of the invention shown in Fig. 4, the arrangement is similar to that of Fig. 2, however the respective deviations Δhi, Δbi of the vertical dimension hi and lateral dimension bi as detected by the vertical dimension detector 31 and the lateral dimension detector 32 respectively from their reference values hiREF, biREF are supplied to a rolling control device 33 and the speed control device 34 respectively, to thereby control the screw position and the speed of the ith mill stand. In Figure 4 are also shown the shape correction device 35 that receives outputs from the rolling or depression control device 33 and the speed control device 34, and calculates the dimensional change value Δhi-1* in the vertical dimension and a change value Δbi-1* in the lateral dimension in the i-1th mill stand 3 such as will reduce the values Δhi and Δbi to zero in accordance with a predetermined algorithm. The remaining elements are equivalent to those shown in Fig. 2. With respect to Figs. 3(a) and 3(b) described above, the present embodiment takes notice of the fact that while the lateral dimension bi changes, the vertical dimension hi does not substantially change at the exit of the ith mill stand in the case where the speed for the ith mill stand is changed, and effects control of the speed of the ith mill stand in order to cancel the change in the lateral dimension bi resulting from the correction of the screw position of the ith mill stand. The control operation of this embodiment will now be described more specifically. (1) Control of the vertical dimension The deviation signal Δhi of the vertical dimension hi of the material at the exit of the ith mill stand 4 detected by the vertical dimension detector 31 from the reference vertical dimension hiREF is supplied to the rolling control device 33. The rolling control device 33 applies PI (predictive integrating) control by calculating a screw position correction signal ΔSi for the ith mill stand such as will reduce the inputted deviation Δhi in the vertical dimension to zero based on the characteristic shown in Fig. 3(a). The screw position correction signal ΔS derived from the rolling control device 33 is supplied to the rolling device for the ith mill stand comprising the thyristor 14, the rolling drive motor 8 and the pulse generator 12 to correct the screw position. The correction for the screw position is carried out until the screw position for the ith mill stand detected by the pulse generator 12 agrees with the screw position correction signal. PI control with the rolling control device 33 may be performed in either a continuous or in a sampling fashion. The mill rigidity control devices 15, 16 apply mill rigidity control (BISRA control) due to the rolling loads detected by the load cells 9, 10 and the object of this control device is to decrease the effect of transmitting dimensional change at the inlet to the exit in each of the mill stands. In this case, where the rolling mill has sufficient rigidity, mill rigidity control is unnecessary. The lateral dimension is changed by applying control over the vertical dimension as described above, and the dimensional change is compensated by control of the lateral dimension as described below. (2) Control of the lateral dimension By correcting the screw position in the control of the vertical dimension, the lateral dimension is also changed. Specifically, the change Δbi in the lateral dimension due to the change ΔSi in the screw position can be represented as: Δbi= δbi δSi · ΔSi where δbi/δSi represents an effect coefficient of the change in the screw position relative to the lateral dimension. The lateral deviation represented by equation (9) can be cancelled by controlling the speed of the stand. The deviation in the lateral dimension relative to the change ΔVi in the stand speed can be represented as: Δbi= δbi δVi · ΔVi Accordingly, the change in the screw position represented by equation (9) can be represented according to equations (9) and (10) as: ΔVi= δbi δSi · 1 δbi δVi · ΔSi By applying speed correction to the ith mill stand based on equation (11), the change in the lateral dimension resulting from the correction of the screw position carried out in the control for the vertical dimension may be eliminated. However, if the value of the effect coefficient in equation (11) is not adequate, or the lateral dimension deviates due to a reason other than the change in the lateral dimension resulting from the correction of the screw position, the deviation in the lateral dimension cannot be compensated completely. In order to avoid this, the speed control device 34 applies speed correction of the ith mill stand 4, for example, by way of PI control based on the deviation Δbi of the actually measured value of the lateral dimension at the exit of the ith mill stand by the lateral dimension detector 32 from the reference value biREF of the lateral dimension. By incorporating a control integration factor (I factor), a speed correction signal as will cause the lateral dimension to agree with the reference value biREF can be output. That is, the speed control device 34 carries out speed correction based on equation (11) and the feed back control for the lateral dimension simultaneously. The speed correction signal ΔVi output from the speed control device 34 is added to the reference speed NiREF of the ith mill stand, and inputted to the thyristor 24 for controlling the speed of the motor 22 for the ith mill stand to change the speed thereof and thus control the tension between the i-1th mill stand and the ith mill stand to thereby compensate the deviation of the lateral dimension. By the control over the vertical dimension and lateral dimension as described, both the vertical and lateral dimensions can be controlled so as to agree with the reference values. (3) Control of the i-1th mill stand The rolling and the speed of the ith mill stand are corrected by the rolling control device 33 and the speed control device 34 as described above. However, if the correction amounts are too great, they result in excessively large changes in the rolling torque and the rolling pressure with respect to the rolling and increase the inter-stand tension (or compressive force) excessively with respect to the speed thereby resulting in a risk of twisting or buckling the rolling material. In order to avoid this, the dimensional deviations Δhi, Δbi of the rolling material at the exit of the ith mill stand and the rolling and speed correction amounts ΔSi, ΔVi for the ith mill stand are inputted to the shape correction device 35 for the i-1th mill stand, and correction for rolling and speed are applied to the rolling control device 36 and the speed control device 37 for the i-1th mill stand in order to change the shape of the rolling material at the exit of the i-1th mill stand. The operation of the shape correction device 35 for the i-1th mill stand is similar to that described heretofore in the previous embodiment. That is, the dimensional deviations Δhi, Δbi of the rolling material at the exit of the ith mill stand 4 are inputted to the shape correction device 35 for the i-1th mill stand, and the device calculates such a change value Δhi-1* in the vertical dimension and a change Δbi-1* in the lateral dimension of the rolling material at the exit of the i-1th mill stand as reduces the dimensional deviation to zero. In a third embodiment of the invention illustrated in Fig. 5, the deviation Δbi of the lateral dimension bi detected by the lateral dimension detector 32 from a reference lateral dimension biREF is supplied only to the shape correction device 35. Further, the deviation Δhi of the vertical dimension hi from the reference value hiREF is supplied to the rolling control device 33 to control the rolling position of the ith mill stand. Also shown are a speed control device 34 receiving a control value ΔSi for the screw position of the rolling control device 33 and acting to correct the rolling speed of the ith mill stand in order to compensate the change in the lateral dimension of the material at the exit of the ith mill stand resulting from the rolling control. The shape correction device 35, as in previous embodiments, receives the control outputs from the rolling control device 33 and the speed control device 34, and deviations Δhi and Δbi of the dimensions of the material at the exit of the ith mill stand 4, and delivers a change value Δhi-1* in the vertical dimension and a change value Δbi-1* in the lateral dimension of the i-1th mill stand 3 such as will reduce the deviation Δhi to zero in accordance with a predetermined algorithm, the previously described algorithms being mentioned as examples. The remaining elements numbered similarly to those in Figs. 2 and 4 perform the same or equivalent functions. One of the features of this invention is to estimate and compensate the change in the lateral dimension of the rolling material when the screw position is changed vertically. Specifically, the vertical dimension of a rolling material 5 is detected by the vertical dimension detection device 31 disposed at the exit of the ith mill stand 4 and the screw position of the mill stand 4 is changed so that the detected dimension may agree with the reference vertical dimension hiREF. However, in a rolling mill of this type, the lateral dimension of the rolling material 5 is changed by this change in the screw position. In order to avoid this, the tension between the upstream stands is controlled by changing the rolling speed as well as the screw position of the stand to thereby compensate the change in the lateral dimension. The reason for controlling the speed as well as the rolling position of the stand was explained previously by way of Fig. 3. Fig. 3(a) shows changes in the vertical dimension hi and the lateral dimension bi at the exit of the ith mill stand in the case where the screw position Si for the ith mill stand 4 is changed, and Fig. 3(b) shows a change in the tension between the i-1th mill stand 3 and the ith mill stand 4, as well as changes in the vertical dimension hi and the lateral dimension bi at the exit of the ith mill stand 4 in the case where the speed ΔVR/VR for the ith mill stand 4 is changed. As can be seen from Fig. 3(b), change in the speed for the ith mill stand 4 causes no substantial change in the vertical dimension hi at the exit of the ith mill stand 4 with only the lateral dimension bi being changed. Accordingly, in order to change the vertical dimension hi at the exit of the ith mill stand 4, it is necessary to control the screw position Si for the ith mill stand 4. Taking note of the fact that the lateral dimension bi changes greatly while the vertical dimension hi does not change substantially at the exit of the ith mill stand 4 in the case where the speed of the ith mill stand 4 is changed, the speed of the ith mill stand 4 is controlled in order to cancel the change in the lateral dimension bi resulting from the correction of the screw position of the ith mill stand. The control means according to this embodiment will now be explained more specifically. In Fig. 5, if the screw position of the ith mill stand is changed so as to attain the relation: Δhi=0, the vertical dimension of the rolling material 5 agrees with the reference value. The deviation Δhi of the vertical dimension hi of the rolling material measured by the vertical dimension detection device 31 from the reference vertical dimension hiREF is inputted to the rolling control device 33 to calculate a difference signal ΔSi for the screw position, which is outputted to the rolling device for the ith mill stand comprising the thyristor 14, the rolling drive motor 8 and the pulse generator 12, for instance, under PI control so as to reduce the difference Δhi to zero. PI control as applied by the rolling control device 33 may be performed either in a continuous or sampling manner. The motor driving thyristor 14 drives the rolling drive motor 7 using the screw position difference signal ΔSi until the screw position signal detected by the pulse generator 12 agrees with the screw position difference signal. The mill rigidity control devices 15, 16 apply mill rigidity control (BISRA control) in the manner described in connection with the second embodiment. Where the rolling mills have sufficient rigidity, mill rigidity control is not necessary. The lateral dimension is of course changed by applying the control over the vertical dimension as described above; and the dimensional change is compensated by control of the lateral dimension as described below. Assuming the lateral dimension is represented by bi, the deviation thereof as Δbi, the inter-stand tension as a, the change therein as Δσ and the average deformation resistance as km, the deviation of the lateral dimension and the change in the interstand tension due to the change in the screw position can be represented as: Δbi bi = ∂bi ∂Si · ΔSi Si Δσ Km = ∂σ ∂Si · ΔSi Si where ∂bi ∂Si · ∂σ ∂Si represents an effect coefficient of the change in the screw position relative to the lateral dimension bi of the material and to the inter-stand tension σ, respectively. The lateral deviation represented by equation (12) can be cancelled by controlling the speed of the stand. Specifically the changes in the lateral dimension of the material and in the inter-stand tension relative to the variation in the stand speed VR can be represented as: Δbi bi = ∂bi ∂VR · ΔVR VR Δσ km = ∂σ ∂VR · ΔVR VR Accordingly, the variation in the stand speed sufficient to cancel the change in the lateral dimension relative to the change ΔSi/Si in the screw position represented by equation ( 12) can be represented according to equations (12), (14) as: ΔVR VR = ∂VR ∂bi · ∂bi ∂Si · ΔSi Si That is, the change in the lateral dimension can be eliminated by varying the speed of the stand by an amount ΔVR/VR for the given change ΔSi/Si of the screw position. The speed control device 34 shown in Fig. 5 applies speed control to the stand, for instance, by way of PI control based on the value determined by equation (14). The speed control device 34 receives the screw position difference signal ΔSi from the rolling control device 33, calculates the speed correction signal ΔVi based on equation (16) and corrects the speed of the motor 22 that drives the ith mill stand 4. Specifically, a speed signal prepared by adding - the speed correction signal ΔVi to the speed reference signal NiREF of the motor 22 is supplied to the thyristor 24, which drives the motor 22 in accordance with the speed signal thus applied. The detection device 26 feeds back the speed of the motor 22. The rolling value and the speed of the ith mill stand are corrected by the rolling control device 33 and the speed control device 34 as described above. However, if the correction amounts are too large, this results in excessively large changes in the rolling torque and rolling pressure as mentioned previously, there by bringing about a risk of twisting or buckling the rolling material. In order to avoid such a danger, the dimensional deviations Δhi, Δbi of the rolling material at the exit of the ith mill stand and the correction amounts ΔSi, ΔVi of the rolling amount and the speed of the ith mill stand are inputted to the shape correction device 35 for the i-1th mill stand, and corrections for rolling and the speed are applied to the rolling control device 36 and the speed control device 37 for the i-1th mill stand in order to change the shape of the rolling material at the exit of the i-1th mill stand. The manner of operation of the device 35 and the i-1th mill stand are as described above, the shape correction device 35 calculating such a change value Δhi-1* in the vertical dimension and a change Δbi-1* in the lateral dimention of the rolling material at the exit of the i-1th mill stand as will reduce the dimensional changes to zero, using a suitable calculation algorithm. In the above embodiment, although the lateral dimension detector 32 is disposed at the exit of the ith mill stand 4 and the deviation Δbi of the lateral dimension of the rolling material at the exit of the ith mill stand or the like is inputted to the shape correction device 35 to calculate the change values Δhi-1* and Δbi-1* in the lateral dimension of the i-1th mill stand, the lateral dimension detector 32 may be omitted and the changes Δhi-1* and Δbi-1* may be calculated in the shape correction device 35 based on the deviation Δhi of the vertical dimension and the control amounts or values ΔSi, ΔVi from the rolling control device 33 and the speed control device 34. As described above, according to this invention, since the lateral dimension of the material at the exit of the ith mill stand is detected and the tension of the material between the i-1th mill stand and the ith mill stand is controlled so the difference between the detected dimension and a reference lateral dimension is reduced to zero, rolling can be performed with dimensional accuracy. In addition, since the above control is combined with a calculation of a change value in the vertical dimension and in the lateral dimension at the i-1th mill stand such as will reduce the change in the lateral dimension at the exit of the i-1th mill stand for the control the screw position of the i-1th mill stand and the tension in the material between the i-2th mill stand and the i-1th mill stand, smooth rolling can be performed at high dimensional accuracy with no danger of twisting or buckling the rolling material. Also, according to this invention, since the vertical dimension and the lateral dimension of a material at the exit of the ith mill stand are detected and the screw position of the ith mill stand and the tension between the i-1th mill stand and the ith mill stand are controlled so that the detected value may agree with reference dimensions while, at the same time such change values in the vertical dimension and in the lateral dimension of the material at the exit of the i-1th mill stand are derived as will reduce the vertical dimension and the lateral dimension of the material at the exit of the ith mill stand to be identical with the reference dimensions, and controlling the screw position of the i-th mill stand and the tension of the material between the 1-2th mill stand and the i-1th mill stand in accordance with the delivered values, rolling can be performed at an extremely high dimensional accuracy. As described above, according to this invention, since the lateral dimension of the material at the exit of the ith mill stand is measured and the position of the ith mill stand is controlled so as to equate the measured vertical dimension with the reference vertical dimension while, at the same time, compensating the change in the lateral dimension of the material resulting from the rolling control by controlling the tension between the i-1th mill stand and the ith mill stand, dimensional control is possible with high accuracy. In addition, since such a change value in the vertical dimension and a change value in the lateral dimension of the i-1th mill stand are calculated as will render the dimension of the material at the exit of the ith mill stand to be identical with the reference dimension and by controlling the screw position of the i-1th mill stand and the tension between the i-2th mill stand and the i-1th mill stand in accordance with the calculated values, dimensional control is possible at an extremely high accuracy with neither great changes in the rolling torque rolling pressure nor with excess inter-stand tension (compressive force).

Claims: 1. A multi-stage continuous rolling machine system comprised of successive mill stands having roll axes alternately oriented substantially perpendicularly to each other and a control system comprising: a lateral dimension detector (32) for measuring a lateral dimension (bi) of material at the exit of an ith mill stand (4); means for determining a lateral deviation (Δ bi) as the difference between said lateral dimension (bi) and a reference lateral dimension (biREF); first tension control means (34) for controlling the tension between first and second mill stands (3,4) for control of said lateral dimension; and depression control means (36) for controlling the depression position of said first mill stand (3), characterized in that: said first mill stand is an (i-1)th mill stand (3) and said second mill stand is said ith mill stand (4); in that shape correction means (35) is provided to receive the output of said tension control means (34) and a signal representing said lateral deviation (Δ bi) and is arranged to compute in dependence thereon a change value (Δ hi-1*) in vertical dimension at said (i-l)th stand (3) and a change value (Δ bi-1*) in lateral dimension at said (i-l)th stand (3) as will reduce said lateral deviation (Δ bi) to zero in accordance with a predetermined algorithm; in that said depression control means (36) is arranged to control the depression position of the (i-l)th stand (3) in accordance with said change value (Δ hi-l*) in the vertical dimension as calculated by said shape correction means (35), and in that second tension control means (37) is provided for controlling the tension between an (i-2)th mill stand and the (i-l)th mill stand in accordance with said change value (Δ bi-1*) in the lateral dimension as calculated by said shape correction means (35). 2. A system according to claim 1 wherein said first tension control means (34) is connected to receive said deviation (Δbi) and is arranged to control the tension between said ith and (i-1)th mill stands to tend to reduce said deviation (Δbi) to zero. 3. A system according to claim 1 or 2 wherein vertical dimension detecting means (31) is provided for measuring a vertical dimension (hi) of material at the exit of said ith mill stand (4) and wherein said shape controlling means (35) is connected to receive a signal representing a vertical deviation (Δhi) as the difference between said vertical dimension (hi) and a reference vertical dimension (hiREF) and is arranged to provide said change values in dependence thereon. 4. A system according to claim 3 wherein further depression control means (33) are connected to receive a signal representing said vertical deviation (Δhi) and are arranged to supply a depression position control signal (ΔSi) for control of the depression position of said ith mill stand (4), to tend to reduce said vertical deviation (Δhi) to zero. 5. A system according to claim 4 wherein said first tension control means (34) is connected to receive said depression position control signal (ΔSi) and is arranged to control said tension in dependence thereon. 6. A system according to claim 4 or 5 wherein said shape correction means (35) is connected to receive said depression position control signal (ΔSi) and is arranged to provide said change values in dependence thereon. 7. A system according to any one of the preceding claims wherein said first and second tension control means (34, 37) are operable to control the speed of a drive motor of the relevant mill stand (3, 4). 8. A system according to any one of claims 1 or 3 to 7 wherein said second tension control means (37) is arranged to control the tension between said (i-1)th mill stand (3) and said ith mill stand (4).

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