The present invention relates to a method for controlling minimum tension rolling at continuous mills. A continuous mill is a mill in which the stock is simultaneously rolled in more than one stands i.e. the distance between the stands is quite less as compared to the length of the whole stock. In such a mill, it is necessary to regulate the volume throughput through each stand as per the desired operating norms, thereby controlling interstand tension. For tension free rolling (Equal volume throughput from each stand): where A1 = Area of cross section of 1th stand (roll gap); V1 = Linear Velocity of the billet at the stand; A1+1 and V1+1 are same for the next stand. As evident, equation (I) can be realised either by controlling A1 & A1+1 (Roll Gap Control) or by controlling V1 & V1+1 , in other words V1 & V1+1 (Speed Control). However, the former control can be exercised only when there is a deviation from the set roll gap. Else, it shall affect the breakdown sequence. Moreover, for different shape rolling sections the effective diameters are different. Therefore, the latter approach is more popular for tension control. Thus tension control connotes a tandemness of material flow amongst all stands and the key to tension control is to sustain this tandemness despite parametric variations. The latter implies all tangible variants such as temperature, grade of the stock, roll gap, input profile, mechanical variants such as roll eccentricity etc. These can be measured up by suitable integro-differential equations. However, parametric variations also encompass certain imprecisions which are difficult to quantify such as subcatenous blow-holes, both instock and interstock variation in lateral temperature profile due to nonunique soaking regimes etc. 2 A more perceptible delineation for understanding of interstand tension/ compression situations is through push-pull concepts. If the succeeding stand is pulling the stock more that what the preceeding stand is able to cater, then we have a situation of tension in that interstand. It implies that there is a deficit of material in It, since the volume taken out by the succeeding stand is more that what supplied by the preceeding stand. Such greater deficits have a possibility of twisting of the stock and underfilling the passes leading to mill jamming and dimensional aberrations respectively. Whreas, If the preceeding .stand is pushing the stock more that what the succeeding stand is able to cater, then we have a situation of compression in that interstand. It implies that there is a surplus of material in it since the volume taken out by the preceeding stand is more that what supplied by the succeeding stand. Such greater surpluses have a possibility of looping of the stock and overfilling of passes leading to mill jamming and dimensional aberrations (fins) respectively. Presently there exists different methods for measurement of tension, whether directly or indirectly, with each method having Its own merit and demerit. For example, the Forward Slip Technique (FST) though highly accurate is expensive and also necessitates accurate assessment of modulus of rigidity at the stock temperature. The Ratio Control Technique (RCT) which is in vogue these days requires mounting of pressure cells in the stands for rolling force measurement; whereas the rolling torque is calculated by the main armature current. Since the latter is the most fundamental parameter of the Current Comparison Technique (CCT), it becomes well obvious the significance of main armature current in tension estimation at continuous mills Techniques of Tension Estimation : (i) CCT: The CCT which has been picked up here offers, a low cost solution for indirect tension measurement. It assumes that the main armature current is a true reflection of the torque requirement and by measuring this current at close intervals periodically and by instantiating them with some biting instances we can have a by and large accurate estimation of the tension. 3 There is no changes in mill structure i.e. no additional mountings (as with FST and RCT). The close monitoring and control of speed and current shifts CCT Into the domain of automation and control to a great extent. In other techniques too, once the tension is measured / estimated state-space control models come into picture with high-level control strategies and process models. The so called limitation of this technique is that it is limited to only head end control i.e. it is not able to handle the turbulences occurring after the head end stabilisation. However; a novel approach has been developed in this work so as to extrapolate CCT over the entire rolling of stock. However, this technique necessitates that there should not be any pseudo current generated due to mechanical obstructions, eccentricity etc. Another advantage of CCT is that it is quite generic, i.e. it can be applied to any type of section without changing the hardware/software or any fresh mounting. (ii) FST: FST is an indirect method based on volume and speed ratios in the roll gap. In simple words, In this method the tension is estimated by measurement of the forward slip in the interstand. After some standard assumptions and approximations it can be shown the following : Where, S (t) = tension in the interstand at any instant T EB = Modulus of elasticity Lo = Strip length between stands v(t) = Linear velocity at entry / exit The stock speed is measured and stored until the strip enters the subsequent stands. For FTC. the control adjusts the speed of the previous stand in such a fashion so as to restore the longitudinal force-free value. These change in velocities are extremely small. Therefore, for error free tension estimation, the velocity measuring equipment should be a highly accurate one. 4 This necessitates use of Doppler velocitimeters each at entry and exit of every stand. For several stands the cost is too high and moreover these remain vulnerable to milt repairs and cobbles. One more difficulty with this technique is that at temperatures above 800°C, it is somewhat difficult to predict EB (iii) RCT: RCT involves measurement of a) rolling force (roll separating force) by pressure cells I pressductors I load cells etc. b) rolling torque by main armature current and /or field current & speed and c) lever arm. The basic principle of RCT is that the ratio of rolling force to deformation torque provides an accurate index of interstand tension. In actual rolling the effect of the deformation torque is much more pronounced on interstand tension than that of the rolling force which itself changes very little. Same modalities of cascaded control is done here too i.e. This ratio is stored in the memory and after the biting of the next stand the previous stand speed is so adjusted so as to restore the ratio value to the previous one. This method is more accurate than CCT, but involves additional mounting of pressure cells etc. This technique is in vogue as evinced in the literature survey. (iv) CMFT: With the advent of mass flow gauges, the tension controlled is achieved through speed adjustments so as to have equal mass throughput from each stand. However, these are very expensive and calls for a lot of improvisation with sections of different shapes. It is also disclosed in "Speed Control of Rolling Mills", Raymond G Brister, Control Techniques Asia Pacific (CTAP) -Singapore, Asia Steel 1996, pp 219 that Control Techniques Asia Pacific (CTAP) Ltd, Singapore, a global exponent of Automation and Control has used current comparison technique for both tension estimation and speed control in rolling mills. Since this work is quite recent (1996), it only evinces that the CCT has its own merits over its sophisticated counterparts viz. FST and RCT. A newly developed 32 bit processor card MD29 enables to transfer 5 many tasks from PLC to drive for faster speed control. It also discusses initial speed setting calculations based upon constant volume throughput. For all these calculations the basic reference is the linear speed of the stock head after the last stand. "Dynamic process modelling for tension control in a merchant bar rolling mill", D.C. McFariane and P.M. Stone, BHP research and new technology, Dimensional Control of rolling mills. London, 11-13 Sep. 1990 emphasises the necessity of a process model for dynamic tension estimator. It blends FST and RCT and along with a Kalman estimator predicts the motor power change as a result of tension changes. It acknowledges CCT, but suggests that its scope is limited to head end control only. The starting point is the ubiquitous dynamic discretised state space model. The whole modeling comprises six modules viz. Speed Control Module, Bar Speed Module, Bar Tension Module, Bar Temperature Module, Roll Separation Force Module and Motor Power Module. The hardware platform is DEC3100 and the software platform is MATLAB. Loopless tension controlled rolling of austentic and ferrite stainless grades in hot strip finishing mill", Drexler et all., V DE, Krupp Stahl, AEG, 4th International Rolling Conference, Deauville, France, 1-3 June 1987 underiines the virtues of loopless / loopertess rolling. Though CCT, FST and RCT have been dealt at length, it is the RCT which has been applied. It opines that one of the disadvantages of CCT is that temperature fluctuations are difficult to compensate for. In the first stage Minimum Tension Rolling (MTC) was first experimented and tried out for the F1 - F2 interstand. Only after its successful stabilisation, it was installed in the mill. "Research and Development of control technology for bar and wire rod rolling, Noguchi et al, Nippon Steel, Nippon Steel Technical Report (53), 45-55 Apr. 1992 discloses multivariable control system for interstand tension taking speed and roll gap as control Inputs. A continuous rolling model and an optimal regulator theory has been used for in-stock dimension control. Also an inter-stock dimensional control system based on profilemeter signal processing and tension-free setup. 6 Thus volume throughout control is effected both through speed and roll gap control. There is a novel presence of hybrid control (both through advanced conventional adaptive controls as well as fuzzy logic based speed control). "Looper-less tension control of a hot strip mill finisher", Akamatsa et al, Nippon Steel and Toshiba, pp 410-417, Proceedings, Internationa! conference on steel rolling, Sep. 29- Oct.4, 1980, Tokyo, Japan describes the looper-less tension control of a hot strip mill finisher. The interstand tension control has been done through looper for conventional hot strip mill finisher. The 6 stand hot strip mill at Muroran works, Nippon Steel was added M stand just before the crop shear, and this became the 7th stand finisher. Looper-less tension control by using FTC (Free Tension Rolling) was adopted to control the tension between M and F1 stand. Here, similar to a mixture of RCT & CCT, a cascaded Torque comparison technique (TCT) has been propounded alongwith measuring roll force. "New tension control system in finishing stands of a hot strip mill", Oishi et at, Nippon steel and mitsubishi, pp 418-427, Proceedings, International conference on steel rolling. Sep. 29-Oct.4, 1980, Tokyo, Japan provides in finishing stands of a hot strip mill, a new tension control system has been theoretically and practically developed to detect indirectly and to control the interstand tension without using looper measurements. This system was tested through the practical rolling in the No. 1 -No. 4 stands of the finishing train of the No.2 hot strip mill at yawata works, Nippon steel corporation. From the results of actual rolling tests, it has become clear that this system presents various improved control characteristics on the viewpoints of dynamic response. It opines that TCT and RCT are more efficacious for the thicker cross sections. It innovates these methodologies by extrapolating it to finishing stands. "A new tension control system for hot strip finishing mill", Hayashi et al, Nippon kokan k.k., pp 101-106, IFAC 1dh Triennial world congress, Munich, FRG, 1987 discloses that by suitably blending FST and RCT, NKK has developed a new 7 tension control method for the hot strip mill and applied it to kelhin works. The behaviour of the interstand tension through looper control was evaluated by simulation and it was concluded that the mass moment of looper inertia should be reduced drastically. To achieve this a full stand looperless rolling technique using statistical technique was developed for the large sectioned material use. For optimal control of the multivariable system least square method along with kalmal filter was used. "Simulation of rolling with tension effects to improve thickness control in hot strip mill". Bertrand et al., SOLMER, INRIA and ISRID. pp 287-295, Proceedings international conference on steel rolling, Sep. 29-Oct.4, 1980. Tokyo, Japan discloses ISRID, France with cooperation of INRIA and SOLMER had developed a mathematical model of the finishing mill of a hot strip mill which has been used in this work. Both head end control and the dynamic mid section control has been dealt here. Strip temperature is considered an important parameter her. "Minimum tension control in finishing train of hot strip mills", Gordon v. Bass and Rudolf Harlmann, Siemens Energy and Automation Inc., Rosewell Ga., Eriangen, West Germany., I & S Engg., Nov. 1987 discloses replacement of loopers by MTC. Superimposed on the main electrical drive control system, it generates the correct cascaded speed control setpoints to control interstand material flow based on tension dependent changes on rolling torque. Each MTC performs sequence control, torque arm determination, tension torque value calculation, PI controller, correction and cascade value output etc. The load torque is determined through the observer model. The rolling torque is calculated by measuring drive speed, armature current and field current. RCT ITCT has been used here. "A computer program for the calculation of roll force and torque with strip tension in cold rolling", T.A. El-Bitar, Central Metallurgical Research and Development Institute (CMDRI). Cairo. Egypt, I & SM, May 1993 focuses on the amount of force and torque applied to the rolls for bringing about the desired thickness of the strip. A theoretical rolling intensive work thus develops a computer program based on certain algorithms. 8 "The automatic tension and gauge control at tandem cold mill", Takaharu et al., Kawasaki steel and research laboratory, hitachi, pp 439-450, Proceedings, International conference on steel rolling, Sep. 29-Oct 4, 1980, Tokyo, Japan discloses mass flow detector used for controlling the mass throughput. It also serves as a basic sensor for tension estimation. For controlling tension speed control selected instead of roll gap control, since the latter was found to be sluggish in Mizushima's tandem rolling mill. "Characteristics of rolling in a continuous Billet mill with drive free vertical rolls", Shikano, Kusaba and Hayashi, R&D, Sumitomo Metal Industries Ltd., ISIJ int., 1991 discloses a unique and quite interesting logistics of a 5 stand H-V-H billet mill, where the, drive free vertical rolls are used as prime movers for some power generation elsewhere. This setup necessitates fluctuating TIC throughout the rolling. Each entry and exit to a stand completely changes the TIC patterns giving rise to the deliberate buckling (due to compression) and skidding (due to tension). The paper describes how to adjust speed in order to control the rolling torque and rolling load dynamically with a buckling estimation by tejamur's formula. However, methodology of speed control has not been described. "Reliable roll force prediction in cold mill using multiple neural networks"; S.Cho. member, IEEE et. al., IEEE transactions on neural networks, vol. 8, no.4, 1997 discloses prediction of roll force using artificial neural network. While several known art of controlling tension of continuous rolling mill stands is in use such known systems suffer in that comparison technique is not for the entire stock. Due to this, the speed adjustments are done only after biting with an assumption that biting conditions hold on till the tail end leaves the stands. Generally, due to operational variances this assumption does not hold on. Thus optimised speed control can not be implemented. It is thus the basic object of the present invention to provide a system for controlling tension in continuous rolling which would be based on the entire stock 9 and provide for both feed back and feed forward control thereby effecting control in tension both in terms of post-facto control after sensing the turbulence due to the parametric variations and also after sensing of the parameters of rolling and net result turbulence to the interstand tension even before the stock Is charged. Another object of the present Invention is to provide a system for controlling tension in continuous rolling which would be adapted to track longitudinally the whole stock to thereby effect the controlling based upon the net turbulence at all times and at all linear positions of the stock. The system would thus provide for control of tension for the entire stock right from head-end to tall-end. Yet further object of the present Invention is to provide a system for controlling tension in continuous rolling which would provide both in-stock control implying control of the present rolled stock with input values of the same stock and inter-stock control implying that the parametric values of the present stock will be utilised in anticipation of the next stock. Yet further object is directed to provide a system for minimum tension controlled continuous rolling which would provide for improvement in length and cross-section of rolled stock and substantially avoid the problems of rejection of finished stock in continuous rolling. Yet further object is directed to provide a system for minimum tension controlled continuous rolling which would avoid problems of operational delay due to looping/twisting of metals during rolling. Yet further object is directed to provide a system for minimum tension controlled continued rolling which would avoid problems of damage of mill equipments injury to persons and ensure safe, smooth rolling and favouring the production process. Thus according to the present invention there is provided a method for controlling minimum tension rolling in continuous casting comprising: 10 identifying zones for tension control by means of analysis of samples of main armature current and stand speed wherein each inter-stand is logically divided into four inter-stand time zones (ITZs) comprising an impact recovery zone signifying the biting turbulence, processing and calculating zones, impact compensation by means for real-time speed connection and gearing up for impact compensation; measuring main armature current to compress the torque requirement; measuring main armature current at close intervals periodically; estimating tension by means of instantiating the said armature values with some biting instances; generating output based on set parameter values by means for effecting head end control and/or dynamic control. In the above-disclosed method of controlling tension both feedback and feed forward control is achieved. The approach to tension control is two fold i.e. feedback or feedforward. The former does not need to know the root cause or the genesis of the parametric variations. Whatsoever may be the cause, the tension will be controlled post-facto after sensing the turbulence due to the parametric variation. The other fold is feedforward control which is anticipative in nature. The rolling parameters are sensed early and their net resultant turbulence to the interstand tension is predicted even before the stock is charged. Since the whole stock is longitudinally tracked, so the controller knows the amount of net turbulence at all times and at all linear positions of the stock. Accordingly, it manipulates the control output (speed or gap) keeping in mind the Total Throughput Time (TTT). TTT is the combined time between the actuating an output signal given by the controller and the realisation of the output in the field equipment. The art of tension control is to shift maximum controls to the feedforward realm so that the turbulences can be nipped in the bud and smooth rolling can take place. However, this necessitates veritable sensing of rolling parameters and accurate tracking of the stock which is certainly challenging. 11 Moreover, it assumes unflinching adherence to standard rolling practices. Majority of the tension control systems are composite i.e. with mixed controls of feedforward and feedback. It is thus possible by way of the method of the invention to successfully extrapolated the control for the entire stock control which means right from head-end to tail-end. In-stock implies controls of the present roiled stock with input values of the same stock; whereas by inter-stock control it is meant that the parametric values of the present rolled stock shall be utilised in anticipation for the next stock. There is to be separate strategies for both in-stock and inter-stock controls. Real-time considerations come for the former in which the control regime is divided into water-tight compartments of certain actions at specific times. Whereas for the latter the turbulences through the entire stock are studied and the speeds are so adjusted (after the exit of the present stock) so as to give a synergetic tuning for the next stock. Zones of Tension Control : Zones are identified by analysis of samples of the main armature current and stand speed in the PLC adapting application software. Based upon type of controls and their specific time windows, each interstand is logically divided into four interstand Time Zones (ITZs) as shown in fig. 2 ITZ 1 is called the impact recovery zone. It signifies the biting turbulence. It starts with the biting instance and ends at that sampling instance, where the software declares that steady state values are achieved by initial condition calculation. This is the zone meant for elimination i.e. the parametric values of this zone are to be discarded for speed control calculations. However, the biting speed drop and impact recovery time for the trial billet are calculated in tills zone. ITZ 2 starts with steady state conditions reached and finishes at that instance where the software declares sufficiency of: steady state values for speed control calculations. ITZ 3 starts with the end of ITZ 2 and finishes at that instance where the software sets up the reference calculated for the drive. ITZ 4 is for Impact Compensation (IC) I speed lead adjustment To increase the life of rolls and to reduce biting turbulence I compression, a preemptive increase (equal to the biting drop) in the drive speed is made just before the biting and that extra bit is withdrawn matching with the recovery characteristics. As stated earlier tine drop and the recovery characteristics are found out from the trial billet. 12 In accordance with a preferred aspect in the method provides for impact compensation/speed lead adjustment comprising: identifying fall in speed of stand with every stock biting and time for recovery by means of monitor; comparing of the drop characteristic with trial billets adapting sensor; generating matching signal reference for actuating the drive for necessary speed adjustments. In accordance with another preferred aspect In the aforesaid the method system is provided with means for feed forward temperature compensation comprising means for spatially and temporally synchronised the temperature profile with the biting. In particular, form such feed forward temperature compensation the system is provided with means to Identify the longitudinal temperature profile of the stock and also means for identifying at identifying the time when such temperature are subjected to different stands ; and means for selecting speed references in anticipation based on the above temperature profile in the respective stands. According to yet further preferred aspect of the present invention the method comprises cobble detection and activation of corrective measures based on mill logistics by means of current detector. According to yet further aspect the method provides control system adapting means for sensor smoothening comprising each net stand sensors having independent current sensors. The details of the invention, its object and advantages are explained hereunder in greater detailed in relation to the non-limiting exemplary embodiments of the control system discussed in relation to the accompanying figures wherein Fig. 1 is a schematic illustration of the hardware and network architecture of the control system in accordance with the present invention. 13 Fig. 2 is an illustration of the four differed interstand zones used in the system of the invention. Fig. 3A to 3C are flow charts of the basic tension control algorithm. Fig. 4 is a flow chart illustrates the speed correction system. Fig. 5 to 8 illustrate typical speed controlling in typical rolling patterns. Fig. 9 is an illustration of the effect of speed change on the various interstands. In the present method of the invention the control system is a realisation of the principle of CCT and its extrapolation to the dynamic overall control. The settled steady state value after the biting turbulence with no succeeding stand loaded is taken as the sacrosanct setpoint. In case if a preceding stand(s) is(are) loaded then the set point shall be logged only after the previous interstand(s) is(are) tension-free after speed readjustments. The final set point is arrived after certain statistical adjustments of the current samples of steady state zone. The no. of samples differ from rolling scheme to rolling scheme. As for the head end control, the head end steady state values after the next stand biting (again after statistical processing) are compared with the original set point are desired speed adjustments are done. Whereas for the dynamic control, the set point remains the same whereas the dynamic current values are processed in short packets and dynamically compared to the set values for TIC estimation in all interstands (Since now all preceding stands are loaded). Now these interstand TICs are multiple setpoints around which the present system is built up. Obviously, the embedded knowledge base of the system bring down these interstand TICs to lowest levels in a 'synergetic manner' by adjustments of the stand speeds. Preferably seven levels of quantisation are provided comprising High Tension (HT), Medium Tension (MT), Low Tension (LT), No Tension (NT), Low Compression (LC), Medium Compression (MC) and High Compression (HC). The analog values attached to these levels have been done after detailed logistics study. The validation of this dynamic tension estimation was by and large done when the improper soaked tail ends exhibited compression. Also, it was found that looping phenomena was concomitant with very high compression. Thus, the CCT was adroitly extrapolated for dynamic control. 14 Features of the system guidance recipe: As shown in fig. 3A, at the start of the operation initiation of 5D current logging is done. In the next step 20 samples or on an average 50 samples are filtered after which this average result is stored as X. After this 6D biting is initiated with respect to 5D and subsequent correction is made. In figure 3B during basic tension control next 50 samples of 1 to 5D are tested and the result is stored as Y. Then the difference is calculated as X-Y. In figure 3C again the next 50 samples of 1 to 5D are tested and the result is stored as Z. After that the difference X-Z. Then the billet end Is crossed to check 9D/7D. if the result is Yes then the program terminates and if No then it is looped back to check for the next 50 samples of 1 to 5D. The first target was to locate No Tension Zones (NTZ), if any. If yes, then the complexity reduces. For example, If there are 1 to n stands {1 to (n-1 ) interstands} and let the pth interstand {p-(p+1 )} with n