|Title of Invention||
AN AUTOMATIC LOOP CONTROL SYSTEM TO CONTROL DEPTH OF LOOP IN A SKELP MILL
|Abstract||An automatic loop control system for controlling the depth of loop in a Skelp mill. The system comprises a loop sensor, microcontroller board, programmable controller and a thyristor converter. The automatic loop control system is useful to delink the tension between roughing stands and finishing stands. The system is fully automatic and does not require any manual intervention. This helps for better control of the mill.|
FIELD OF INVENTION
The present invention relates to an automatic loop control system for controlling the depth of loop in a skelp mill, during rolling of hot skelp bar into skelp. The control system would enable automatic control of the depth of the loop and would thus be simple and no operator is required to operate.
BACKGROUND OF THE INVENTION
In a Skelp Mill, Skelp of different widths varying from 140 mm to 310 mm are rolled from skelp bars. The skelp bars are fed to the reheat furnace and after requisite heating, are rolled in 5 roughing and 6 finishing stands. After rolling from finishing stands are over, adjacent metals goes to two beds alternatively, Skelp is coiled in coiler. There is one coiler in each bed.
There is a cobble shear and a looping trough in between roughing group and finishing group. Vertical downward loop is formed between two adjacent horizontal stands and loop depth is be maintained to roll without tension. Control of loop depth is also necessary to prevent entry of folded skelp in cobble shear and horizontal stand.
Loop depth is generally controlled manually from pulpit by observing the loop. Such conventional manually operated system for loop control suffers from drawbacks / disadvantages which are discussed hereunder:
A. Manual control requires continuous attention of the operator.
B. In case of tension in the bar, there is a tendency of roll breakage of a
horizontal stand as it is pulling the bar from the previous horizontal stand.
C. In case of excess loop, cobble will takes place, resulting in mill delays.
OBJECTS OF THE INVENTON
It is thus basic object of the present innovation to provide an automatic loop control system at the looping trough in a skelp mill.
Yet another object of the present invention is to provide a low cost solution in an existing rolling mill to have a facility of automatic loop control mechanism.
A further object of the present invention is to provide automatic loop control system that will remove errors caused due to human intervention.
SUMMARY OF THE INVENTION
Thus according to the present invention there is provided an automatic loop control system for skelp mill comprising:
means for measuring the depth of the loop and generating a signal;
means for processing the said signal and generating a reference voltage;
means for receiving the reference voltage and changing the speed of the finishing
A loop sensor is used in measuring the depth of the loop. The loop sensor comprises a high gain amplifier and suitable lens for measuring the depth of the loop from a distance of about 9 m. The signal generated by the loop sensor is fed to a microcontroller board and a programmable controller for processing of the signal. The microcontroller receives two analog signals, one for loop reference voltage and the other for loop depth and generates a control voltage output. The programmable controller receives the control voltage and generates the reference voltage. The reference voltage is then fed to the thyristor converter for changing the speed of finishing stands. The thyristor converter is provided with a finishing stand speed regulation system which along with the thyristor converter controls the speed of the control stands.
The automatic loop control system of the invention basically utilizes (i) loop sensor, (ii) Power supply for loop sensor, (iii) Microcontroller hoard, (iv) Power supply for microcontroller board, (v) Programmable LOGIC controller PLC and (vi) a thyristor converter for generating DC power for the motors
The loop sensor comprises
(i) An array of infra red photo detector with electronics to output analog voltages suitable for the process requirement
The power supply for loop sensor comprises
(i) One power supply to generate 5 V regulated DC power (ii) One power supply to generate + 12 V regulated DC power
The microcontroller board comprising
(i) Processor 89C52 with 11.0592 MHz crystal, 8 channel analog to digital converter, 3 channel digital to analog converter, 32 digital input and outputs, RS 232 serial communication link
(ii) Watch dog timer for automatic reseting The Programmabte LOGIC Controller PLC comprising (i) Analog inputs and Digital inputs (ii) Analog output
5 The Thyristor converter comprising
(i) Thyristor sets to convert 3 phase AC power to variable DC power
The automatic loop control system thus provides
(i) Automatic control of loop at the looping trough as per the set value
(ii) Communicates with a PC to show the depth of the loop and loop reference voltage.
The system also provides information in a computer for better monitoring of the process.
DESCRIPTION OF PREFERRED EMBODIMENT
The details of the invention, its objects and advantages are explained in great detail in relation to non limiting exemplary embodiments of the control system of the invention in relation to the accompanying figures wherein
Fig 1 shows the mill layout where automatic looping control system is implemented.
Fig 2 is a general arrangement of the control system with all its components in relation thereto;
Reference is first invited to Fig 1 where general arrangement of Skelp mill is shown.
The roughing group consists of 9 rolling stands. Hot skelp bars are drawn out from the furnace by draw out roller mechanism. There are six horizontal stands (H1 to H6) and three vertical stands (E1 to E3) also called edger. A cobble shear is located after H6 stands, which cut the skelp bar during cobble. There is a plate called looping trough between H6 and H7. The front end of the skelp will pass through the top of
the plate and enters into H7 stand. After biting of H7 stand the looping trough goes down and allows the skelp bar to sag downward called loop. The operator from pulpit decreases the speed of finishing group so that a loop of certain depth is formed in the looping trough. During rolling, if there is excess load in the finishing group, there
will be speed drop of finishing group and depth of the loop will increase. In that case the operator will increase the speed of finishing group to maintain the loop to a certain depth. However, if the speed of finishing group is increased, the depth of the loop will be less and the operator will decrease the speed of finishing group. Finishing group consists of five horizontal stands H7 to H11. There are three photocells PC1, PC2 and PC3 located after H2 stand, H5 stand and after the looping trough. The loop sensor is located 9 meter away from the rolling line. The purpose of keeping the loop sensor at a distant place is to keep the sensor safe. Normally these sensors are mounted below the pulpit so that hitting by overhead crane can be totally avoided.
There are two DC buses called roughing group bus and finishing group bus. All the roughing group stand motors are connected with the roughing group bus and the finishing group motors are connected with finishing group bus. Motor speed is varied by varying the bus voltages. All motors are DC motors with separately excited field. There is a provision for changing the individual motor speed by varying the field current.
Thus to increase the finishing group speed the operator actually increases the finishing group voltage and thereby speed of all the stands are increased by same
Fig 2 shows the scheme of implementation of automatic loop control system. The following are the components of the control system;
(i) Loop sensor
(ii) DC power supply PS1 and PS2 for loop sensor
(iii) Microcontroller board based on 89C52
(iv) Switch Mode Power Supply for Microcontroller board
(v) Programmable Controller C
(vi) Thyristor converter for generating bus voltage.
7 Loop Sensor
The sensor consists of (i) Lens system, (ii) an array of Germanium Infra-red photocliode, (iii) Signal processing electronics, (iv) An EPROM containing a look up table to suit the process requirement and (v) Output circuits. The lens system is used so that the image of the hot object, which forms the loop, falls on the diode array. For a movement of 500 mm in the loop the image shifts by 25 mm. Each diode develops a small emf when radiation in the range of 800-1800 nm falls on it. This emf is amplified by a high gain, frequency compensated amplifier. The output is then compared with a threshold voltage. The digital output of the comparator is fed to a memory device (EPROM), where a look up table is stored. The EPROM generates 8-bit binary output that corresponds to the depth of loop stored in the pit. The buffered binary output is available for control of a digital drive which finally controls the depth of the loop. The digital output is converted to an analog output (0 to -10 V DC) for analog control purposes. The sensor is installed below pulpit, around 9000 mm away from the loop.
DC power supply PS1 and PS2 for loop sensor
There are two numbers of regulated power supply PS1 and PS2 for loop sensor. PS1 generates 5 V DC while PS 2 generates + 12 V DC. The 5 V power supply has a capacity of 1 A and + 12 V power supply has a capacity of 0.5 A. Input to this regulated power supply is 230 V AC, 50 Hz.
The microcontroller board is based on 89C52 processor (ATMEL make) where there is on chip 8K EEPROM to store the application program. There is on chip 128 KB of data memory to store intermediate values.
The following subsystems are available on the board:
o Crystal 11.0592 MHz
o Real Time Clock DS 1287
o 8 channel analog to digital converter, - 5 V to + 5 V DC, 12 bit, using AD574
o 3 channel digital to analog converter, -5 V to + 5 V DC, 12 bit, using AD 7521
o 3 channel timer/ counter, 16 bit, using 8253
o 8 digital input through DIP switch
o 24 digital input / output.
o RS 232 serial output using MAX 232
o RS 485 serial output using 75176
There are two analog inputs and one digital input to the board. There is one analog output and one digital output from the board. The inputs and outputs are described as below:
Analog Input 1 (Al~1) :
Loop sensor output is connected in this channel. Sensor output is 0 to -10 V. This voltage is divided by two equal resistance such that the final output is 0 to -5 V DC. This voltage is fed to channel 0 of the Analog to Digital Converter. This signal is denoted as Vf.
Analog Input 2 (AI-2) :
The loop reference voltage is connected in this channel. Loop reference voltage is 0 to + 5 V DC corresponds to 0 to 500 mm of depth of the loop. This voltage is fed to channel 1 of the Analog to Digital Converter. This signal is denoted as Vr.
Digital input 1 (Dl-1)
There is one digital input to the system. The digital input is generated in the Programmable Controller. This input is generated when PC 1 is high followed by PC 2 is high followed by PC 3 is high and looping trough is down.
Analog output 1 (AO-1)
The microcontroller generates one analog output corresponds to the given equation:
Controlled Output = (- Vf - Vr) X Gain
Gain is set by thumb DIP switch.
Gain = (binary equivalent of decimal number set by DIP switch /16 )
The analog output is in the range of - 5 V DC to + 5 V DC.
Digital output 1 (DO-1)
This digital output is shown by a LED. As long as this LED is glowing, CPU is functioning and system is healthy. If this LED does not glow, it may be assumed that CPU has halted or there is some hardware fault.
Communication to PC
The CPU outputs a signal through RS 232 port which is connected to a PC where the status of all the signal can be seen.
The processor is having a watch dog timer. As long as the CPU is running and executing the application program a pulse is available from CPU. This pulse from CPU resets a counter. As long as the counter is reseted cyclically, counter reading can not go high. If pulse is not available from CPU then counter reading goes to high value and this high value resets the CPU 89C52. The reset pin of 89C52 processor is pin # 9. This pin is normally kept at low value by a pull down resistance of 8.2 K A high, Logic '1' on this pin resets the processor. While the application program is running, if CPU halts or if it is in an infinite loop then the processor gets reseted by a high pulse available from counter.
The microcontroller board is having a 11.0592 MHz crystal which generates the clock for this IC. From this basic clock processor generates time delays.
Switch Mode Power Supply for Microcontroller board
This power supply generates 5 V DC and + 12 V DC for microcontroller, input to this power supply is 230 V AC, 50 Hz.
Programmable logic Controller (PLC)
Programmable controller receives the controlled output from the microcontroller board. The reference voltage for thyristor converter is generated in the Programmable controller. The Programmable Controller outputs 0 to + 10 V DC which is fed to the converter block.
Thyristor converter for generating bus voltage.
The thyristor converter generates 0 to 800 V DC corresponds to 0 to 10 V DC reference. This DC voltage feeds the finishing stands motors. Motor speed is proportionate to the DC bus voltage.
The system of the invention is thus a cost effective solution for automatic looping control in a Skelp mill.
1. An automatic loop control system to control the depth of the loop comprising :
means for measuring the depth of the loop and generating a signal;
means for processing the said signal and generating a reference voltage;
means for receiving the reference voltage and changing the speed of finishing stands.
2. An automatic loop control system as claimed in claim 1, wherein the means
for measuring the depth of loop is a loop sensor.
3. An automatic loop control system as claimed in claim 2, wherein the loop
sensor comprises a high gain amplifier and suitable lens for measuring the
depth of the loop from a distance of about 9 m.
4. An automatic loop control system as claimed in claim 1, wherein the means
for processing the signal comprises a microcontroller board and a
5. An automatic loop control system as claimed in any one of the preceding
claims, wherein the said microcontroller board is adapted to receive two
analog signals, one for loop reference voltage and the other for loop depth
and to generate a control voltage output.
6. An automatic loop control system as claimed in any one of the preceding
claims wherein the said programmable controller being adapted to receive the
control voltage and generate the reference voltage.
7. An automatic loop control system as claimed in claim 1, wherein the means
for changing the speed of finishing stands is a thyristor converter.
8. An automatic loop control system as claimed in any one of the preceding claims, wherein the thyristor converter is provided with a finishing stand speed regulation system which along with the thyristor converter controls the speed of the control stands.
An automatic loop control system for controlling the depth of loop in a Skelp mill. The system comprises a loop sensor, microcontroller board, programmable controller and a thyristor converter. The automatic loop control system is useful to delink the tension between roughing stands and finishing stands. The system is fully automatic and does not require any manual intervention. This helps for better control of the mill.
|Indian Patent Application Number||594/CAL/2002|
|PG Journal Number||49/2007|
|Date of Filing||21-Oct-2002|
|Name of Patentee||STEEL AUTHORITY OF INIDA LIMITED|
|Applicant Address||RESEARCH & DEVELOPMENT FOR IRON AND STEEL, DORANDA, RANCHI 834002, STATE OF JHARKHAND.|
|PCT International Classification Number||B21 B-37/00|
|PCT International Application Number||N/A|
|PCT International Filing date|