Claims:WE CLAIM:
1. An improved control system for single stand hot and cold rolling mill comprising:
at least one digital DC drive with incremental encoder for main mill motor;
at least two DC drives of individual screw down motors;
at least two absolute encoders for position feedback of the screw down;
at least two load cells for roll force measurement and at least one torque sensor for measurement of shaft torque;
PLC system for interfacing the drives, field instruments and a control desk such as to control the mill operation in hot and cold rolling modes.

2. The system as claimed in claim 1, wherein said PLC system is operatively connected to receive input from one or more field devices, control desk and generate command to the DC drive of mill motor and screw down for operation as per the logic Optionally including workstation and user interface for remote monitoring, operation and data logging of the mill.

3. The system as claimed in anyone of the claim 1 or 2, wherein the absolute encoders feedback position of the screw down to the PLC system and based on the position of the screw down the PLC system generates command to the individual DC drives for facilitating synchronized operation of the screw down without using magnetic clutch;
said individual absolute encoder indicating position of the individual screw down to the PLC which generates the reference speed to the individual drives to catch up the other up with the screw down which is leading.

4. The system as claimed in anyone of the claims 1 to 3, wherein the torque sensor attachment is adapted to adjust and measure the shaft torque while rolling in hot and cold mode for both 2-Hi and 4-Hi respectively.

5. The system as claimed in anyone of claims 1 to 4, wherein the digital DC drive with incremental encoder interface with the PLC system for precise speed control of the mill motor.

6. The system as claimed in anyone of the claims 1 to 5, comprises two numbers laser based LVDT sensors in conjunction with a hydraulic system for bottom rolling balancing of the mills wherein, the hydraulic system provides for lifting the bottom roll through hydraulic cylinder at two ends of the roll and the laser sensor at the two ends records linear displacement of the bottom roll to facilitate bottom rolling balancing and eliminating the bottom roll eccentricity.

7. A method for automatically setting roll gap for different passes during rolling in the single stand hot and cold rolling mills comprising
measuring position of operator and drive side screw down through absolute encoder installed with screw down motors;

receiving of the position of both side screw down, in PLC and calculating the exact linear position of both the screw down with reference to top limit switch;

generating PLC based command to both side screw down drives to be at the desired position;
tuning of drive acceleration and deceleration time for the screw down to stop at the desired position;

providing feedback of position control of the screw downs with the help of absolute encoder thereby setting of roll gap as per predefined roll gap for different passes.
, Description:FIELD OF THE INVENTION:
The present invention relates to an improved system for control of single stand rolling mill. More particularly, the present invention relates to an improved control system based on Programmable Logical Controller (PLC), Digital drives and a new set of instruments, for controlling the single stand mill operation in hot rolling mode and cold rolling mode.

BACKGROUND ART.:
Single stand rolling mills are either meant to roll hot rolled slabs or cold rolled sheets/plates metals. This single stand hot and cold rolling experimental mill is versatile in the manner that it can be used both for hot and cold rolling operations with change in mill configuration i.e 2-Hi and 4-Hi. Normally, such single stand hot and cold rolling mills are used as experimental mills for material characterisation, product development, process optimisation, defect analysis, model development and development of new rolling lubricants through simulation of hot and cold rolling process.
However, due to obsolescence such old single stand hot and cold rolling mills are prone to frequent failures of mill drives and control system, jamming of screw-down system and misbehaviour of roll balancing system. With these problems, it was also not possible to simulate hot rolling conditions properly as strain and strain rate were restricted to very low levels. The mill was also facing instrumentation problems with respect to measurement and recording of various rolling parameters.
There are patents for method for operating a rolling mill for warm and cold rolling flat products such as Application number EP19980107702. The method concerns operation of a mill for hot and cold rolling of flat products in single or multiple arrangements of roll stands with two or more rolls. Control of the roll gap takes place with correction of the force difference between the roll drive and operator ends, and compensation of the settings correcting the bending and balancing forces. The method is characterised by the fact that the control system has an additional corrective quantity formed through measurement of the horizontal forces on all individual rolls.
Thus there has been a need for developing a low cost system for controlling the rolling mill parameter of single stand experimental rolling mill based on the screw down position, roll force applied by screw down, mill motor control and use of LVDT sensor in conjunction with the existing hydraulic system for bottom roll balancing.

OBJECT OF THE INVENTION:
The basic object of the present invention is develop a control system for single stand hot and cold rolling mills which would be adapted to run the mills avoiding the failures of mill drives and related control system, jamming of screw-down system and misbehaviour of roll balancing system.
Another object of the present invention is to provide an improved low cost control system for single stand hot and cold rolling mills which would be adapted to automatically set roll gap for different passes during rolling according the input thickness of the feedstock and desired output thickness.
Further object of the present invention is to provide an improved control system for controlling synchronized movement of drive side and operator side screw down motors without magnetic clutch.
Yet another object of the present invention is to provide a control system for main mill motor speed control during hot rolling and cold rolling mode.
Further object of the present invention is to provide an improved system for bottom rolling balancing using LVDT sensor in conjunction with the hydraulic system.
Yet another object of the present invention is to provide an improved system for recording the important parameters like shaft torque, roll force, roll gap, motor current, and sample temperature while rolling in hot and cold rolling modes to study the mechanical properties with respect to the rolling conditions.

SUMMARY OF THE INVENTION:
The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the present invention. It is not intended to identify the key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concept of the invention in a simplified form as a prelude to a more detailed description of the invention presented later.
According to basic aspect of the present invention there is provided an improved control system for single stand hot and cold rolling mill comprising:
at least one digital DC drive with incremental encoder for main mill motor;
at least two DC drives of individual screw down motors;
at least two absolute encoders for position feedback of the screw down;
at least two load cells for roll force measurement and at least one torque sensor for measurement of shaft torque;
PLC system for interfacing the drives, field instruments and a control desk such as to control the mill operation in hot and cold rolling modes.

According to another aspect in the present system, the PLC system is operatively connected to receive input from one or more field devices, control desk and generate command to the DC drive of mill motor and screw down for operation as per the logic Optionally including workstation and user interface for remote monitoring, operation and data logging of the mill.

According to a further aspect in the present system, the absolute encoders feedback position of the screw down to the PLC system and based on the position of the screw down the PLC system generates command to the individual DC drives for facilitating synchronized operation of the screw down without using magnetic clutch;
said individual absolute encoder indicating position of the individual screw down to the PLC which generates the reference speed to the individual drives to catch up the other up with the screw down which is leading.

According to another aspect in the present system, the torque sensor attachment is adapted to adjust and measure the shaft torque while rolling in hot and cold mode for both 2-Hi and 4-Hi respectively.

According to another aspect in the present system, the digital DC drive with incremental encoder interface with the PLC system for precise speed control of the mill motor.

According to yet another aspect, the present system comprises two numbers laser based LVDT sensors in conjunction with a hydraulic system for bottom rolling balancing of the mills wherein, the hydraulic system provides for lifting the bottom roll through hydraulic cylinder at two ends of the roll and the laser sensor at the two ends records linear displacement of the bottom roll to facilitate bottom rolling balancing and eliminating the bottom roll eccentricity.

According to another aspect in the present invention, there is provided a method for automatically setting roll gap for different passes during rolling in the single stand hot and cold rolling mills comprising
measuring position of operator and drive side screw down through absolute encoder installed with screw down motors;

receiving of the position of both side screw down, in PLC and calculating the exact linear position of both the screw down with reference to top limit switch;

generating PLC based command to both side screw down drives to be at the desired position;

tuning of drive acceleration and deceleration time for the screw down to stop at the desired position;

providing feedback of position control of the screw downs with the help of absolute encoder thereby setting of roll gap as per predefined roll gap for different passes.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
The following drawings are illustrative of particular examples for enabling the present invention, and are not intended to limit the scope of the invention. The drawings are not to scale and are intended for use in conjunction with the explanations in the following detailed description.

Figure 1 illustrates Control Architecture for Single stand rolling Mill in accordance with the present invention.

Figure 2 illustrates the Automatic Roll gap setting for different Passes of the Mill in accordance with the present invention.

Figure 3 illustrates the synchronized movement of screw down without magnetic clutch in accordance with the present invention.

Figure 4 illustrates the Main Mill Control with speed feedback control using incremental encoder in accordance with the present invention.

Figure 5 illustrates the Data Logging Facilities of various parameters while rolling in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS:
The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.
The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.
It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.
Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments.
As mentioned herein above, the present invention relates to an improved Control system for single stand rolling mill hot and cold rolling modes. In hot rolling mode the mill is 2-Hi while in cold rolling mode the mill is 4-Hi. During hot rolling there are two rolls having diameter of 350mm while in cold rolling two more works rolls are inserted with diameter of 150mm.
The present system consists of the one number of four quadrant digital DC drive of Mill motor , two numbers of four quadrant digital DC drive for Screw down motors, one number of Programmable Logic controller (PLC), two numbers of load cell on each side of screw down, two number of absolute encoder on each side of screw down, one number of torque sensor , one number of incremental encoder , one number of PC based operator’s interface and one control desk with remote Input and output module, touch panel for the operator’s interface with the mill. The schematic of the new control system architecture is shown in Figure 1. The Programmable Logic controller is installed in the new Control Room. The Electrical panels with the DC drive regulator and convertor is installed in the mill floor. The control desk having panel view and selector switches and push buttons for automatic and manual control of the mill during rolling is installed in front of the mill. The field instruments like load cells, absolute encoder, incremental encoder, torque sensor are installed in the mill. The drives, control desk and field instruments are interfaced with the PLC through control, signal and communication cable as required.
In one embodiment, as shown in figure 2, the automatic roll gap adjustment is done through the HMI screen in the Panel view installed in the control desk. The roll gap for different passes is set in the HMI screen. The operator selects the pass number and the roll gap is obtained as per the set point. The individual screw down drive gets the common command from PLC based on the feedback from the absolute encoder for the linear movement of the screw down to the set position. This is a low cost method for adjustment of the roll gap for each pass specially for the mill which are meant for experimental purpose and not for production purpose. Figure 3 illustrates the synchronized movement for both the screw down which is required for maintaining uniform roll gap in the mill. In the prior art, provision of magnetic clutch was there. This clutch was energized when the joint linear movement of screw down was in required to be done. In case of unsynchronized movement, the common screw down drive used to get stalled when ever there was tilt alarm. In the present art, the magnetic clutch is removed and the screws down motors have been provided with individual drives. The individual drive gets the common command from PLC for the individual screw down to be at the set position. Each screw down motor stops at the set position. The stalling due to tilt alarm is not required in such case and the magnetic clutch is not required.
In another embodiment illustrated in Figure 4, the requirement of precise control of mill motor speed is achieved through use of incremental encoder. The speed feedback control loop of the DC drive can be achieved through the armature emf method. To achieve the precise speed control, incremental encoder has been used with zero speed switch. The speed reference is given from the operator desk having Panel View for monitoring and control of the main mill motor speed as per the requirement of the mill. The mill speed is varied from 0-30 mpm for hot rolling mode and can be varied upto 60 mpm in cold rolling mode.
In another embodiment, two numbers of laser based LVDT sensor have installed below the bottom roll. These sensors provide the linear position of the back-up roll and are used to check the eccentricity of the roll at the final position.
In another embodiment, as illustrated in Figure 5, there is provided a data logging system which provides the various parameters like, roll force , torque , roll gap , mill speed, etc which are necessary for studying the mechanical characteristic of the sample after rolling with respect to the rolling mill. Based on these studies , the rolling procedures are formulated for any production mill to get the desired mechanical characteristic after rolling.