CLIAMS:1. A system for non-contact online billet length measurement and identification of billets beyond a predefined length comprising
non contact type laser based distance measurement sensors including at least two laser sensor devices for measuring the billet length at charging grate before feeding to heating furnace;
said laser sensor devices focussed on cross-sectional face of the billets for facilitating accurate measurement of the length of the billets;
PLC system including PLC processor cooperative to the laser sensor devices for receiving distance information from the laser sensor devices and then processing the information in the PLC processor to calculate actual billet length and identify any billets beyond a predefined length.

2. A system as claimed in claim 1 comprising
mounting structure housing said laser sensor devices focussed on cross-sectional face of the billets for facilitating accurate measurement of the length of the billets while said billets are closely spaced at the charging gate.

3. The system as claimed in anyone of claims 1 or 2, wherein the laser sensor devices selected based on billet material to be sensed, temperature of the material, ambient temperature, configurable range, accuracy, measuring distance having preferably +/- 3 mm accuracy and 10 meter sensing range.

4. The system as claimed in anyone of claims 1 to 3 , wherein the two laser sensor devices are focused on both cross sectional faces of the billets and the laser sensor devices measure the distance between the sensor head and the cross-sectional face of the billets.

5. The system as claimed in anyone of claims 1 to 4, wherein the mounting structure comprises structure platform for placing the laser sensor devices and a slotted hole on the structure platform for tightening the laser sensor devices with the structure platform through a single bolt.

6. The system as claimed in anyone of claims 1 to 5, wherein the laser sensor devices are adapted to move through the slotted hole for enabling movement of laser beam of the sensor devices in right or left directions for ensuring focusing of the sensor devices on the cross-sectional plane of the billets.

7. The system as claimed in anyone of claims 1 to 6, wherein the sensor devices height adjusting arrangement to move the sensor laser beam up or down keeping the base fixed.

8. The system as claimed in anyone of claims 1 to 7, comprises cooling jackets provided with each of the sensor devices including water and air line for cooling and purging the sensor devices at the charging grates.

9. The system as claimed in anyone of claims 1 to 8, wherein the PLC system cooperative to the laser sensor devices receive the analog signals from two laser sensor devices though an Analog input/ output module.

10. The system as claimed in anyone of claims 1 to 9, wherein the PLC processor of the PLC system is configured for measuring the billet length based on the analog signals from two laser sensors come to the PLC system and distinguish one billet from the subsequent closely spaced billets in the charging gate and achieve desired accuracy in measuring length of the billets irrespective of it unevenness in the surface finish.

11. The system as claimed in anyone of claims 1 to 10, wherein the PLC system is disposed in operative communication with a Digital output module and BCD unit for displaying the billet length as determined by the PLC system.

12. The system as claimed in anyone of claims 1 to 11, wherein the Digital output module comprise LED based indicator for informing user for corrective action when determined billet length exceeds the predefined set value of billet length and rejecting particular billet from feeding to the heating furnace.
,TagSPECI:FIELD OF THE INVENTION:
The present invention relates non-contact online length measurement of moving metal billets. In particular, the present invention is directed to develop a non-contact online measurement of the billet lengths and identification of the longer billets. The system of the present invention is particularly adapted for measuring the billet lengths in reheating furnace feeding area of a typical steel processing mill.

BACKGROUND ART:
In a typical steel processing plant, the reheating furnace feeding area preferably comprises of two charging grates with a billet rejecter in each of the charging grate followed by a roller table section for feeding billets of required size to the reheating furnace for heating of billets before rolling or any subsequent operation. The billets are placed on the charging grates which are operated from individual control pulpit by cranes. These billets serially move on the charging grates and finally pushed to roller table which feeds the billets to the reheating furnace. The charging grate is shown in Figure 1.
Now feeding of the Billet system to the furnace is very critical for running of the steel processing plant since these are critical equipment for production of the steel article. Also it is most important that the billets which are to be fed into the furnace should not be more than the specified length (11.8 m). Over sized billets are being supplied by the mother unit. Earlier defective & longer billets charged to the furnace were identified manually. Incorrect and untimely detection of longer billets resulted in furnace jamming which leads to furnace delay, damage of refractory and hampering of production.
Existing length measurement system involving non contact type sensors such as laser velocimeter, laser distance measurement are not particularly adapted for measuring the billet length on the charging grate where billets are closely placed side by side and indentify any particular billet with improper length from the closely spaced billets.
Thus, there has been a need for developing a non contact type length measurement system which will be specifically designed to measure the billet length on the charging grate where billets are closely placed side by side and identify billets with improper length.

OBJECTS OF THE INVENTION:
It is thus the basic object of the present invention to develop a system which would be adapted to measure billet length and identification of longer billets in a charging grate of a steel processing plant.
Another object of the present invention to develop a non contact length measurement system which would be adapted to measure the billet length on the charging grate where billets are closely placed side by side and identify billets with improper length.
Yet another object of the present invention to develop a system which would be adapted to accurately measure the billet length irrespective of the billets unevenness in the surface finish.

SUMMARY OF THE INVENTION:
Thus according to the basic aspect of the present invention, there is provided a system for non-contact online billet length measurement and identification of billets beyond a predefined length comprising
non contact type laser based distance measurement sensors including at least two laser sensor devices for measuring the billet length at charging grate before feeding to heating furnace;
said laser sensor devices focussed on cross-sectional face of the billets for facilitating accurate measurement of the length of the billets;
PLC system including PLC processor cooperative to the laser sensor devices for receiving distance information from the laser sensor devices and then processing the information in the PLC processor to calculate actual billet length and identify any billets beyond a predefined length.

According to another aspect, the present system comprises a mounting structure housing said laser sensor devices focussed on cross-sectional face of the billets for facilitating accurate measurement of the length of the billets while said billets are closely spaced at the charging grate.

According to another aspect in the present system, the laser sensor devices selected based on billet material to be sensed, temperature of the material, ambient temperature, configurable range, accuracy, measuring distance having preferably +/- 3 mm accuracy and 10 meter sensing range.

According to a further aspect in the present system, the two laser sensor devices are focused on both cross sectional faces of the billets and the laser sensor devices measure the distance between the sensor head and the cross-sectional face of the billets.

According to yet another aspect in the present system, the mounting structure comprises structure platform for placing the laser sensor devices and a slotted hole on the structure platform for tightening the laser sensor devices with the structure platform through a single bolt.

According to a further aspect in the present system, the laser sensor devices are adapted to move through the slotted hole for enabling movement of laser beam of the sensor devices in right or left directions for ensuring focusing of the sensor devices on the cross-sectional plane of the billets.

According to another aspect in the present system, the sensor devices includes height adjusting arrangement to move the sensor laser beam up or down keeping the base fixed.

According to another aspect, the present system comprises cooling jackets provided with each of the sensor devices including water and air line for cooling and purging the sensor devices at the charging grates.

According to a further aspect in the present system, the PLC system cooperative to the laser sensor devices receive the analog signals from two laser sensor devices though an Analog input/ output module.

According to a further aspect in the present system, the PLC processor of the PLC system is configured for measuring the billet length based on the analog signals from two laser sensors come to the PLC system and distinguish one billet from the subsequent closely spaced billets in the charging grate and achieve desired accuracy in measuring length of the billets irrespective of it unevenness in the surface finish.

According to yet another aspect in the present system, the PLC system is disposed in operative communication with a Digital output module and BCD unit for displaying the billet length as determined by the PLC system.

According to a further aspect in the present system, the Digital output module comprise LED based indicator for informing user for corrective action when determined billet length exceeds the predefined set value of billet length and rejecting particular billet from feeding to the heating furnace.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES:
Figure 1 shows a charging grate in a steel processing plant for feeding billets of required size to the reheating furnace for heating of billets.
Figure 2 shows a schematic representation of the present system for monitoring length of billets while feeding in the reheating furnace.
Figure 3 shows sensor mounting structure of the present system (a) top view and (b) side view.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING FIGURES:
The present invention discloses a system for non contact online cold billet length measurement and identification of longer billets in hazardous area of rolling mills specifically in the charging grate where the billets are closely placed before feeding to the heating furnace.
The system of the present invention basically comprises non contact type distance measurement sensors, power supply units, PLC system and adjustable mounting structure with cooling jackets for protection of sensors.
The integrated scheme for measurement of billet length at charging grate by involving the system of the present invention is illustrated in the accompanying figure 2.
As shown in the refereed figure, the present integrated scheme for measurement of billet length at charging grate includes PLC system, sensor devices, BCD unit and annunciation.
In the present system two laser based distance sensor devices are used for measuring the billet length at the charging grate of the before feeding to the heating furnace. The quality of the laser sensor devices are selected based on the material to be sensed, temperature of the material, ambient temperature, configurable range, accuracy, measuring distance etc. It is preferred to use laser based length measurement sensor devices of +/- 3 mm accuracy, 10 meter sensing range (because as per site condition measuring distance was varying between 2 to 7 meters) and other specification meeting required conditions.
As discussed herein above the billets are closely spaced at the charging grate, thus to properly measure the length of the billets in this condition the laser sensor devices of the present system are focussed on the cross-sectional face of the billets. In particular, the two laser sensor devices are focused on both cross sectional faces of the billets. These sensor devices measure the distance between the sensor head which is installed in a fixed location and the cross-sectional face of the billets.
The sensor devices are installed over a mounting structure. A schematic representation of the mounting structure is shown in the accompanying figure 3. As shown in the figure 3, the height of the mounting structure (3) is adjusted depending upon the height of centre of billet cross section from the 0 level. As per illustration of the figure 3, the sensor devices (2) are placed on the structure platform (1) and it is tightened through a single bolt on a slotted hole on the structure platform (1). Due to vibrations or other factors when sensor devices gets out of focus, the sensor devices (2) is moved through the slotted hole to move the laser beam in right or left directions for refocusing the sensor devices on the cross-sectional plane of the billets. The sensor base is fixed so it cannot move it up/ down direction so for that there is inbuilt arrangement in the sensor devices itself to move the sensor laser beam up/ down keeping the base fixed.
A cooling jacket is also provided with each of the laser sensor devices. It comes with cooling and purging facility. The cooling jacket is also provided with water & air line for cooling and purging the laser sensor devices at the charging grates.

The PLC system cooperative to the laser sensor devices receive the analog signals from two laser sensor devices though an Analog input/ output module. The Analog input/output module is preferably a configurable type because data acquisition can be done in any form of analog input (4-20 mA, 0-10 V DC etc.).
The distance information is then processed in the PLC system to calculate the actual billet length. The PLC processor of the PLC system is configured for measuring the billet length based on the analog signals from two laser sensors come to the PLC system. The PLC processor is also configured to distinguish one billet from the subsequent closely spaced billets in the charging grate and achieve desired accuracy in measuring length of the billets irrespective of it unevenness in the surface finish.
In the present system, the point of laser focus is selectively chosen such that it can be pointed exactly centre of the billet cross section. The exact operation of the charging grate is such that operator initiates a command to complete one cycle of charging grate. In one cycle, focused billet will move completely further and billet which was in backward position come in front of laser beam and measurement being done.. For uneven surface of billet accurate measuring laser sensor is sufficient to measure the exact billet length.
The PLC system of the present system is connected with a Digital output module for displaying the billet length as determined by the PLC system in the BCD unit & sending signal to annunciation.
The BCD unit is selected based on the number of digits to be shown and LED lamp annunciation is selected which is compatible to our digital output signal.
For displaying length, once the PLC calculates actual length of the billet, another PLC routine is written which converts the real value into the binary coded value which gives the digital output corresponding to the actual length and this value is being displayed in the BCD unit through the Digital output module.
For annunciation, once the PLC calculates actual length of the billet, a PLC routine is written which continuously monitors the actual billet length calculated by PLC system. If the actual billet length exceeds the predefined set value (upper limit) of billet length it generates output and compatible LED lamp will blink in front of operator and operator will take the corrective action and that particular billet will be rejected by the operator.
Therefore the present invention implements a state of art distance measurement system with sensors and PLC (Programmable Logic Controller) system for measuring accurate billet length at charging grates and display of length in BCD (Binary Coded Decimal) display unit. The system of the present invention also reduces the down time of the steel processing mill and also increasing life of reheating furnace because damage of refractory due to jamming of long billets has been reduced.