CLIAMS:1. A system for controlling billet distribution and feeding mechanism for multi strand wire rod mill comprising
motor driven distribution table for selecting strand into which the billet is to be fed and thereby delivering the same to the selected strand in conjunction with motor driven draw out roller and solenoid operated pinch rolls;
position measuring means for measuring position of the distribution table and speed measuring means for measuring speed of the motor for driving the distribution table;
VVVF Drive unit for operating the moving distribution table in a controlled manner;
PLC based control unit having operative connectivity with billet distribution and feeding mechanisms of the distribution table, draw out rollers, pinch rolls, operative connection to operator desk for controlling operation of the billet distribution and feeding mechanisms, the VVVF Drive unit for moving the distribution table and other associated field control circuits, for controlling all the operations in an integrated manner.

2. The system as claimed in claim 1, wherein said operative connectivity comprises Ethernet connectivity between the PLC based control unit and Remote I/O nodes, Profibus connectivity with VFD and hardwired connections from field control circuits, devices and operator desk to Remote I/O nodes.

3. The system as claimed in any one of claim 1 or 2 wherein the position measuring means of the distribution table includes high resolution absolute encoder with SSI interface for measuring position of the distribution table in real time and continuously feed backing the table position to the control unit.

4. The system as claimed in anyone of claims 1 to 3, wherein the motor for driving the distribution table includes Squirrel cage Induction motor driven by the VVVF drive unit.

5. The system as claimed in anyone of claims 1 to 4, wherein the speed measuring means for measuring the speed of the motor includes hollow incremental encoder for measuring speed of the motor driving the distribution table in real time and continuously feeding back the motor speed to the control unit.

6. The system as claimed in anyone of claims 1 to 5, wherein the control unit computes complete logic for operation of the distribution table including calculation of instantaneous table position, calculation of speed set point for the motor, logic of operation for bypassing of different strands and selecting any particular strands.

7. The system as claimed in anyone of claims 1 to 6, wherein the control unit computes the logic of operation for bypassing of different strands and selecting any particular strands by involving billet status in furnace, readiness of the billet ejecting means in the distribution table, readiness of down line equipment in each of the strand and permission for rolling.

8. The system as claimed in anyone of claims 1 to 7, wherein the PLC based control unit with Ethernet connectivity is disposed in operative connection with the distribution table in Profibus protocol by involving Fibre Optic or Cat 6 network for driving the distribution table based on the computed logic for operation of the distribution table.

9. The system as claimed in anyone of claims 1 to 8 comprises temperature sensors for continuously monitoring the temperature of the distribution table and its motor operating in close proximity to furnace of the strands of the wire rod mill.

10. The system as claimed in anyone of claims 1 to 9, comprises distribution table drive changeover means to ensure highest availability of the system in the event of failure of primary drive equipment.

11. The system as claimed in anyone of claims 1 to 10, wherein the PLC based control unit is adapted to be disposed in operative communication with a remote user interface for facilitating on-line overview of billet feeding operation and controlling the billet distribution and feeding mechanism from a centralized remote location.
,TagSPECI:FIELD OF THE INVENTION:
The present system relates to controlling and managing Billet distribution and feeding into a multi strand Wire Rod Mill. In particular the present invention is directed to develop an improved system for accurate measurement and control of Billet Distribution and Feeding mechanism for multi strand Wire Rod Mill. The system of the present invention advantageously replaces the outdated combination of CAM Limit switch and Slip ring motor for Billet Distribution System and the outdated control scheme for billet distribution and feeding mechanism, with the state of art system comprising of highly accurate PLC based control, Variable Frequency drive and measurement devices. The developed system can be adapted for many similar applications of distribution and feeding of steel or other stocks or multiple positioning of equipment operating at a high speed.

BACKGROUND ART.:
Billet distribution and feeding into a multi strand Wire Rod Mill is accomplished with the help of Draw Out Roller (DOR), Distribution Table (DT) and Pinch Rolls (PR). The strand into which the billet is to be fed is first selected by the DT. DOR is a single roller at the bottom of the roll table. Pinch Rolls for individual strands clutch the billet from top and pull it into the corresponding strand in Rolling Stand 1. All the operations are carried out from an operator desk. The number of operations per hour is generally not less than 120 per hour. Layout of equipment and summary of operations for multi-strand mill (here, 4 strand mill is shown) is given in Figure 1. Another view is given in Figure 2.
The Billet distribution and feeding system is very critical for running of the Mill since these are the common equipment for all four strands. Therefore, 100% availability of these equipment has to be ensured. Secondly, accurate positioning of Table for feeding of billets is essential owing to the very small gap left on sides of billet. Any side-ways deviation of the billet can result in cobble at entry and therefore stoppage of production. Further, control systems and their electrics in a Wire Rod Mill are distributed over a large area.
The existing system for billet distribution and feeding operation in the multi strand Wire Rod Mill is given in Figure 3. The existing system was based on Slip ring motor for driving DT including frequent starts/stops, CAM limit switch for DT position feedback, solenoid operated Pinch Rolls, AC motor driven DOR and an obsolete operator desk. All interconnections were through large number of power and control cables running from control desks to machine hall control panels. The existing control system for the above equipment was based on hardwired relay logic circuits. The billet pushing operation is carried out by a different operator than the one carrying billet feeding operation. The coordination between these operators was through manual signalling system where by the billet feeding operator gives permission through indication, to push billet. No other interlock to prevent wrong pushing or feeding was incorporated.
As described above, billet distribution and feeding operation is achieved through a set of mechanisms comprising of DT, DOR and PRs. Also coordination is required between billet pushing operation and billet distribution & feeding operation. In the existing system, distribution table (DT), is the most complex mechanism. The positioning of DT was carried out through an outdated system which did not deliver the desired accuracy and repeatability in positioning and also required frequent maintenance and adjustments for proper positions. The components of the existing system and the drawbacks are as follows:
CAM Limit switch for DT Position feedback: This is a contact type switch which gives information only about discrete positions reached and not any intermediate values. This makes fine tuning of the system for position and speed corrections difficult. The adjustment of positions is done by manually rotating the mechanisms and setting. This is prone to error because this is purely based on human estimation. Secondly, being contact type switch, this is prone to frequent failures and also maladjustments.
Slip ring motor for Driving DT: Slip ring motors are obsolete AC motors used earlier for achieving frequent starts/ stops and manual acceleration/deceleration of equipment through rotor resistance control. These motors have now become obsolete. Further, no provision for speed feedback was available making motor speed control difficult to achieve. There was also a 220Vdc operated mechanical brake to hold the motor stationary.
The operator desk through which the complete operation was carried out was old and did not have any status indications, due to which operator did not get any feedback about the mechanisms.
All interconnections among the components were through large number of control cables running from control desks to machine hall control panels prone to fire hazards in the congested cable galleries and earth faults. This resulted in disruption of production process and contributed to mill downtime in a major way.
The existing logic and control system for the above equipment was based on oldest hardwired relay logic circuits, using relays as the control and logic devices, and using wires for the interconnections between the relays to realize the control logic of operation. The system was time-consuming to set up and fault-find, had no flexibility in terms of logic modifications and due to the large number of contacts and interconnections, was unreliable.
The other equipment which form an integral part of the billet distribution and feeding system comprise of AC motor driven DOR and AC solenoid operated PR(s). These were also hardwired system with commands hardwired from operator desk to relay logic based circuits and hence difficult to maintain.
As described earlier, integrated billet pushing, billet distribution and billet feeding operation is desirable for efficient rolling and to prevent cobbles. In existing system, the coordination between operators for billet pushing and billet distribution & feeding was through manual signalling system, where by the billet feeding operator gives permission through indication, to push billet. No other interlock to prevent wrong pushing or feeding was incorporated resulting in wrong pushing & feeding of billets leading to breakdowns, mechanical damage of equipment and delays.
The existing system, since based on relay logics did not have state of art on-line monitoring and fault diagnostic facilities resulting in tedious maintenance and delays in liquidation of faults, again contributing to reduction of mill efficiency.
Thus there has been a need for developing system for managing Billet distribution and feeding into a multi strand Wire Rod Mill which will solve the above mentioned operational limitations of the existing billet distribution and billet feeding operating, controlling and managing system.

OBJECT OF THE INVENTION:
It is thus the basic object of the present invention to develop a system which would be adapted to accurately control billet distribution and feeding mechanism for multi strand wire rod mill.
Another object of the present invention is develop a system for controlling billet distribution and feeding mechanism for multi strand wire rod mill which would be adapted to involve PLC based control unit, VVVF Drive unit, industrially proven speed & position feedback devices as well as a new control desk for billet distribution and feeding mechanism.
A still further object of the present invention is develop a system for controlling billet distribution and feeding mechanism for multi strand wire rod mill which would be adapted to easily and accurately calibrate and control the billet distribution and feeding mechanism from a remote centralized location.
Yet another object of the present invention is develop a system for controlling billet distribution and feeding mechanism for multi strand wire rod mill which would be adapted to compute logic of integrated operation for bypassing of different strands and selecting any particular strands based on billet status in furnace, readiness of the billet ejecting and pushing means in the distribution table, readiness of down line equipment in each of the strand and permission for rolling.

SUMMARY OF THE INVENTION:
Thus according to basic aspect of the present invention, there is provided a system for controlling billet distribution and feeding mechanism for multi strand wire rod mill comprising
Motor driven distribution table for selecting strand into which the billet is to be fed and thereby delivering the same to the selected strand in conjunction with motor driven draw out roller and solenoid operated pinch rolls;
position measuring means for measuring position of the distribution table and speed measuring means for measuring speed of the motor for driving the distribution table;
VVVF Drive unit for operating the moving distribution table in a controlled manner;
PLC based control unit having operative connectivity with billet distribution and feeding mechanisms of the distribution table, draw out rollers, pinch rolls, operative connection to operator desk for controlling operation of the billet distribution and feeding mechanisms, the VVVF Drive for moving the distribution table and other associated field control circuits, for controlling all the operations in an integrated manner.

According to another aspect in the present system, the said operative connectivity comprises Ethernet connectivity between the PLC based control unit and Remote I/O nodes, Profibus connectivity with VVVF Drive unit and hardwired connections from field control circuits, devices and operator desk to Remote I/O nodes.

According to another aspect in the present system, the position measuring means of the distribution table includes high resolution absolute encoder with SSI interface for measuring position of the distribution table in real time and continuously feed backing the table position to the control unit.

According to yet another aspect in the present system, the control unit computes complete logic for operation of the distribution table including calculation of instantaneous table position, calculation of speed set point for the motor, logic of operation for bypassing of different strands and selecting any particular strands.

According to a further aspect in the present system, the motor for driving the distribution table includes Squirrel cage Induction motor driven by a VVVF drive unit.

According to another aspect in the present system, the speed measuring means for measuring the speed of the motor includes hollow incremental encoder for measuring speed of the motor driving the distribution table in real time and continuously feeding back the motor speed to the control unit.

According to a further aspect in the present system, the control unit computes the logic of operation for bypassing of different strands and selecting any particular strands by involving billet status in furnace, readiness of the billet ejecting means in the distribution table, readiness of down line equipment in each of the strand and permission for rolling.

According to another aspect, the present system comprises temperature sensors for continuously monitoring the temperature of the distribution table motor operating in close proximity to furnace of the strands of the wire rod mill.

According to yet another aspect, the present system comprises distribution table VVVF drive unit changeover means to ensure highest availability of the system in the event of failure of primary drive equipment.

According to a further aspect in the present system, the PLC based control unit is adapted to be disposed in operative communication with a remote user interface for facilitating on-line overview of billet feeding operation and controlling, calibrating and fault finding in the billet distribution and feeding mechanism from a centralized remote location.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES:
Figure 1 and Figure 2 shows layout of equipment and summary of operations in multi strand Wire Rod Mill of a steel processing plant.
Figure 3 shows the block diagram and interconnection scheme of the existing system for billet distribution and feeding operation in the multi strand Wire Rod Mill.
Figure 4 shows the block diagram of the system for billet distribution and feeding operation in the multi strand Wire Rod Mill in accordance with the present invention.
Figure 5 shows configuration of Billet Distribution System in accordance with the present invention.
Figure 6 shows interconnection schemes for drive, encoder and temperature sensor changeover in accordance with the present invention.
Figure 7 shows mounting arrangement for DT motor and encoders in accordance with the present invention.
Figure 8 shows an HMI screen giving on-line overview of billet distribution and feeding operation in accordance with the present invention.
Figure 9 shows calibration of distribution table for positioning from a centralized location.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING FIGURES:
As stated herein above, the present invention discloses a new and advanced system for accurate measurement and control of Billet Distribution and Feeding mechanism for multi strand Wire Rod Mill. The system of the present invention includes a PLC and Networking architecture with remote I/Os, improved control desks and other accessories, replacing hardwired interconnections from Desks to Control panels and relay logic based outdated interlocking schemes of the mechanisms of system. The block diagram of preferred embodiment of the present system is given in Figure 4.
The distribution table is the most complex mechanism of billet feeding system from the point of view of measurement and control. The mechanism has close to 120 operations per hour and very short travel range from one position to the next and at a high speed. The outdated hardwired control system comprised of CAM Limit switch, used for obtaining feedback about the table reaching any of the final positions where the billet is to be fed, and Slip Ring AC motor for driving the table and an electromechanical DC operated brake. This mechanism operates in conjunction with the AC motor driven Draw out roller and DC solenoid operated Pinch Rolls. The desk for operation of distribution table, draw out roller, pinch rollers, strand bypass commands, other auxiliary controls for furnace door operation, permission for billet pushing and so on was hardwired to relay panels in machine halls. In the present invention, the system is completely revamped to PLC based control unit and industrially proven speed & position feedback devices as well as a new control desk. Configuration of Billet Distribution System is depicted in Figure 5. The existing slip ring motor for driving the distribution table was replaced with new heavy duty Squirrel cage Induction motor driven by a VVVF drive unit. To measure the actual position of DT at any point of time, an absolute encoder with SSI interface has been used to sense table position in real time. Speed feedback to the VFD is through a hollow incremental encoder. A Drive Changeover scheme has been provided in the event of failure of primary drive to ensure highest availability of the equipment. The interconnection schemes for drive, encoder and temperature sensor is given in Figure 6. The VFD-PLC stations are networked over Profibus protocol. A new operator desk with enhanced facilities for status indication was also installed.
To design an integrated automation and control system, architecture with PLC and distributed I/Os over an industrial network backbone is adopted. Distributed Inputs/Outputs panels herein referred to as Remote I/O (RIO) nodes were strategically installed near the operator posts for billet feeding operation. The system is built over PLC Processor and Remote I/Os platform on Ethernet TCP/IP through Fibre-Optic Cable and CAT6. Two RIO nodes enabled streamlined interface of I/Os from field desks, machine hall electrics and interface panels using only a single length of industrial, armoured communication cable. The implementation of a reliable network based PLC system drastically reduced the problem of cable damage in congested cable galleries, cable faults and frequent mal-operation of equipment due to hardwired connections.
The billet distribution and feeding operation involves very complex operative sequences, taking into consideration billet status in furnace, billet ejector readiness, readiness of down the line equipment in each strand and permission for rolling. Based on this, the strand into which the billet has to be fed is automatically selected and the table positioned accurately. The strands not ready for rolling are to be automatically bypassed. All these operations are very fast owing to high speed of rolling. Logic for interlocks is implemented in the PLC and set point and command for the drive are given from PLC through Profibus network. Complete logic for operation of the Distribution table including calculation of instantaneous table position, calculation of speed set point for motor, logic of operation in case of bypass of different strands and other appropriate interlocks have been incorporated for foolproof operation of the system.
There was a severe space constraint for erection of new motor and encoders that required measures such as Hollow type encoder for speed, careful engineering for matching of foundation of existing motor, Brakes, retrofitting position encoder over existing shaft of CAM limit switch etc. Mounting arrangement for DT motor and encoders is given in Figure 7.
Criticality of the system warranted that a reliable MIS system with user friendly diagnostic facility for quick trouble shooting and on-line monitoring is implemented. An HMI station and communicating on-line with the PLC and Drive system was specially designed for the purpose. Features of the system include node and equipment diagnostics, mill operation information, event alarms, historical trends for vital parameters and so on. Figure 8 shows an HMI screen (user interface) giving on-line overview of billet feeding operation. Status of complete integrated billet feeding process is available to monitor the inter-pulpit coordination for feeding billets and appropriate interlocks built into the program to prevent wrong feeding of billets. The distribution table can also be now easily calibrated for positioning from a remote centralized location (Figure 9). These measures have helped in providing an efficient maintenance and operation management system to reduce downtime in this critical section of mill.
The billet feeding equipment and drives are just at the exit of the furnace. The arduous site conditions of high temperature and conductive dust necessitated very careful selection of electronic equipment suitable for installation in the area (e.g. IP67 measurement devices and Motors, Temperature resistant Signal cables, FO Networks). Specially designed dust proof field RIO panels and enclosures with cooling arrangement were designed and fabricated for long term sustainability.
Therefore, the present system which broadly includes
i. PLC & Remote I/O based automation system with Ethernet communication network from PLC-RIO-HMI communication and Profibus DP interface for PLC-Drive communication, having Cold redundancy through Fibre Optic/Cat 6 network and industrial grade networking accessories.
ii. Remote I/Os for operator desk and interfaces of Motor control panels (MCPs) in Machine Hall.
iii. New operator desk with on-line status indications.
iv. Interface to the Motor control panels (MCPs) of DOR and PRs .
v. New scheme for DT based on VVVF drive and new Squirrel Cage Induction motor with Drive Changeover facility. Existing electro mechanical brake was retained. Positioning of the DT was accomplished through position feedback from new absolute encoder connected to RIO through SSI interface and speed feedback taken through new incremental encoder. Existing mechanical system including gear system was retained.
vi. HMI terminal in the DAS room for monitoring of the various parameters of the new system.
vii. Programming, testing and monitoring of all the nodes through portable laptop based PLC programming terminal and Drive programming terminal.
viii. The operator commands for operation of any of the mechanism is given from the operator desk. These signals hardwired to Remote I/Os, are transmitted to the PLC through network.
ix. The logic for processing outputs (Control & Indications) are built in the PLC. The command outputs are interfaced to existing motor control panels through interfacing contactors and relays for DOR & through new Drive for DT.
provides a clear advancement over prior art with respect to following aspects
Accurate Measurement and Control of Distribution Table Position with user friendly calibration.
Reliable scheme for signal interfacing and controls of distributed equipment, operator desk and control panels using PLC and Networked Architecture.
Integrated Control of Draw Out Roller, Strand Pinch Rolls and Distribution table alongwith other associated operations.
Optimization of billet feeding speed through closed loop VVVF control.
Elimination of wrong feeding of billets through software interlocks and Enhanced operation monitoring and maintenance management through user friendly HMI.