Claims:WE CLAIM

1. A system for synchronized movement of the two arms of a mechanism driven by individual motor and coupled to the common slab pushing arm and the said system comprising of :
a Programmable Logic Controller (PLC) means installed in the control panel for storing the logic for the synchronized movement of the individual arms of slab kick off mechanism;
a pair of absolute encoder installed on the output shaft of gear box connected with the individual DC motor;
a pair of incremental encoder installed on the non-driving end of the motor shaft of the individual motor;
at least one digital drive panel means installed in the control panel for each arm of slab kick off motor;
a rotary limit switch means installed on the output shaft of gear box of the each arm of slab kick off mechanism; and
a control panel including PLC and a plurality of screens installed for viewing the amount of skew between the two arms of slab kick off mechanism from remote location.

2. The system as claimed in claim 1, wherein the a Programmable Logic Controller (PLC) means is configured for providing the speed reference to each drive panel of the individual arms of slab kick off mechanism based on the amount of skew between the two arms of slab kick off mechanism.

3. The system as claimed in claim 1, wherein the absolute encoder is configured for sending the position (in counts) of the individual arms of slab kick off mechanism to the Programmable Logic Controller (PLC) through communication cable.

4. The system as claimed in claim 1, wherein the incremental encoder is configured for sending the motor speed (in rpm) to its own DC drive panel.

5. The system as claimed in claim 1, wherein the digital drive panel means is configured for generating the firing angle for the convertor of that motor based on the

speed reference given by the Programmable Logic controller through the communication cable connecting the drive panel to the PLC.

6. The system as claimed in claim 1, wherein the rotary limit switch means is configured for giving the forward and reverse limit position.

7. The system as claimed in claim 1, wherein the a control panel including PLC is configured for real time view of motor current , speed and the position of the two arms of slab kick off mechanism from remote location.

8. The system as claimed in claim 1, wherein the under condition of fault in absolute encoder, for synchronized movement of the two arms of slab kick off mechanism driven by individual motor, corrective signals are provided using at least two incremental encoder (speed control loop & position control through calculated value), at least two rotary limit switch (for Forward & Reverse reference position) and at least two Digital DC drive and one PLC.

9. The system as claimed in claim 1, wherein the common arm of the slab kick off mechanism is flexibly coupled to the two arms of the slab kick off in case of mal- operation and skew between the arms is beyond a prescribed safe limit.

10. The system as claimed in claim 1, wherein the real time control and monitor of the amount of skew in the two arms of the slab kick off mechanism is carried out through the control panel in the pulpit.

Dated; this 10th day of July, 2017.

(N. K. Gupta)
Patent Agent,
Of NICHE,
For SAIL

To,
The Controller of Patents,
The Patent Office, Kolkata.
, Description:A SYSTEM FOR SYNCHRONIZED MOVEMENT OF THE TWO ARMS OF A MECHANISM DRIVEN BY INDIVIDUAL MOTORS.

FIELD OF THE INVENTION

The present invention relates to a system for synchronized movement of the two arms of a mechanism driven by individual motors. More particularly, the present invention relates to a scheme for synchronized movement of two arms of a mechanism driven by individual motors and flexibly coupled to a common load arm so that the skew between the arms is within a prescribed safe limit.

BACKGROUND OF THE INVENTION

Research & Development Centre for Iron and Steel (RDCIS), Ranchi and Bokaro Steel Plant (BSL), Bokaro have designed, installed and commissioned “An improved system for the synchronized movement of the two arms of slab kick off mechanism driven by individual DC motor and coupled to the common slab pushing arm.” This system is being utilized successfully since commissioning from March 2017 at Hot Strip Mill (HSM), Bokaro Steel Plant.

Hot Strip Mill of Bokaro Steel Plant has four slab re-heating furnaces to heat the slabs received from Continuous Casting Shop (CCS) or Slabbing Mill (SM). The slabs received from SM and CCS are stored in slab yard of HSM. These are then transferred on slab car in pile comprising three- four slabs. From the slab car it is transferred to the de-piler which is adjacent to the roller table. The slab kick off mechanism pushes the slab kept on the de-plier on to the roller table one by one. From the roller table it is moved in front of the designated re-furnace and then pushed into the furnace through the pusher mechanism. To cater to the four re-heating furnace of HSM there are three numbers of slab kick off mechanism. Two are for cold slabs which come from CCS and kept in the three bays of HSM slab yard. They are designated as 1st Cold Charging (5A-5B) & 2nd Cold Charging (1A-1B). The third is

for hot charging for the slabs which are returned back to re-heating furnace due to improper heating or which come from Slabbing Mill. It is designated as hot charging mechanism (7A-7B).

The slab kick-off mechanism has two arms which are coupled mechanically to a common pushing arm. Each arm is driven through individual 60kW DC motor through rack and pinion & gear box. In the prior art the linear movement of both the arms was synchronized through syncro transmitter/receiver called selsyn. The controller panel interfaced with selsyn is analogue type. The DC drives were also of analogue type. Speed control of the DC motors was done through armature EMF feedback which is not very accurate. Moreover, due to unreliable operation of the selsyn, there was a regular problem of the synchronization of the arms. The arms got skewed frequently as a sequel to which the slab was not placed in proper orientation on the roller table. The orientation of the slab had to be set right manually which affected the productivity of the mill. The selsyn and the DC drive were of USSR make which were old and obsolete. The procurement of the selsyn had become problematic as they were no more being manufactured by the OEM or elsewhere. The analogue DC drives too gave frequent problems due to obsolescence.

The present inventors have successfully designed, installed and commissioned an improved system for synchronized movement of the two arms of the slab kick off mechanism using DC drives, PLC, new control desk, rotary limit switch, absolute encoder and incremental encoder.

OBJECTS OF THE INVENTION

One object of the present invention is to overcome the disadvantages / drawbacks of the prior art.

Therefore such as herein described there is provided a synchronized movement of the two arms of slab kick off mechanism driven by individual motors and coupled to the common slab pushing arm and the said system comprising of : a Programmable Logic

Controller (PLC) means; an absolute encoder which is substantially installed on the output shaft of gear box connected with the individual DC motor; an incremental encoder installed on the non-driving end of the motor shaft of the individual motor; a digital drive panels means is installed in the electrical control room for each arm of slab kick off motor, a rotary limit switch means installed on the output shaft of gear box of the each arm of slab kick off mechanism and a remote control panel means installed to in the electrical control room configured for controlling the overall system from a remote location.

The primary object of the present invention is to provide a system for synchronized movement of the two arms of slab kick off mechanism driven by individual motor and coupled to the common slab pushing arm, using absolute encoder (for position control loop), incremental encoder (for speed control loop), rotary limit switch (for Forward & Reverse reference position), Digital DC drive and PLC.

Another object of the present invention is to provide an alternative scheme for synchronized movement of the two arms of slab kick off mechanism driven by individual motor using incremental encoder (speed control loop & position control through calculated value), rotary limit switch (for Forward & Reverse reference position), Digital DC drive and PLC in case of fault in absolute encoder.

Yet another object of the present invention is to provide a scheme for auto correction of skew in the two arms of the slab kicks off in case of some mal-operation by the operator

Yet another object of the present invention is to provide a scheme for protection of the common arm of the slab kick off mechanism flexibly coupled to the two arms of the slab kick off in case of some mal-operation by the operator and skew between the arms is beyond a prescribed safe limit.

Yet another object of the present invention is to provide features of controlling and monitoring the amount of skew in the two arms of the slab kick off mechanism through the operator’s control desk in the pulpit.

These and other advantages of the present invention will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING

Other features as well as the advantages of the invention will be clear from the following description In the appended drawing:

Figure 1 illustrates pictorial view of individual Arms of slab kick off coupled to the common slab pushing arms in accordance with the present invention;

Figure 2 illustrates the schematic view of the interface of various equipments &

instruments with PLC in accordance with the present invention;

Figure 3 illustrates the pictorial view of the connection of incremental encoder to DC

motor in accordance with the present invention;

Figure 4 illustrates the pictorial view of the absolute encoder & rotary limit switch connected output shaft of gear box in accordance with the present invention;

Figure 5 illustrates the electrical control panel for slab kick off arm position in accordance with the present invention;

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and illustrate the best mode presently contemplated for carrying out the invention.

The present invention relates to an improved system for synchronized movement of the two arms of slab kick off mechanism driven by individual motor and coupled to the common slab pushing arm.

The present system consists of a PLC for storing the logic for synchronized movement of the two arms of the slab kick off mechanism driven by individual motor and coupled to a common load pushing arm as shown in Figure 1. This figure illustrates the configuration of Slab kick-off mechanism showing the individual arms connected to common pushing arm. Each individual arm is driven by 60kW DC motor. The slabs are placed on de-piler and from the de-piler it is pushed on to the roller table by the slab kick off common arm.

The PLC is connected to the drive panel, the absolute encoder, incremental encoder, drive panel, rotary limit switch, control post and PC based engineering workstation including the interface of equipments and instruments with the PLC as per the scheme shown in Figure 2. The drive panels are connected to PLC through communication cable (profibus cable), the absolute encoder is connected to PLC via hardwired signal cable. The incremental encoder is connected to the drive panel. The control panel and PC based engineering work station is connected to PLC via Ethernet cable. The control desk is connected to PLC via control cable.

In the new scheme the existing two numbers of DC motors were retained. A new digital DC drive panel for each motor has been installed for speed control. The two DC drive panels are connected with the PLC through communication cable. Each DC drive panel is connected to an incremental encoder for giving speed back of the motor. The

connection of incremental encoder to motor and it’s mounting on the non-driving side of the motor is shown in Figure 3. The incremental encoder also gives the position of the individual arms of slab kick off mechanism based on calculated values. The calculation is done in the PLC based on the gear ration, load wheel diameter and the motor speed. The output shaft of the gear box through its reduction gear is connected to an absolute encoder and rotary limit switch as shown in Figure 4, which depicts the installation of absolute encoder on the output shaft of the gear box and the mounting of encoder and limit switch on the reduction gear box shaft. The absolute encoder gives the position of the individual arms of slabs kick off mechanism to PLC. Depending upon the forward or reverse movement and the position of the arms with respect to each other, the PLC gives the signal to the individual drives to accelerate or decelerate in order to decrease the amount of skew between the two drives. The feedback of forward and reverse limit or forward and reverse home position to PLC is through the rotary limit switch. Two numbers of contacts have been used for the forward and reverse limit in the DI card of PLC. At the reverse limit switch or reverse home position, the absolute encoder counts are reset since at this position both arms are in same position i.e. the skew is not there between them. Secondly, when the forward limit is operated, the forward movement of the drive motor is stopped through PLC and similarly for the reverse limit. This feature is a safety so that the motor does not over travel in forward or reverse direction. As an alternative to the scheme for synchronized movement of arms of slab kick off through absolute encoder, we have in the logic a scheme for synchronization through incremental encoder. In case of failure of absolute encoder, the selection of absolute encoder in PLC can be made false and then the synchronization between the arms of slab kick off mechanism will be through the calculated value of the position of the arms in the PLC based on motor speed feedback by incremental encoder, the load wheel diameter and the gear box ratio.

The movement of the arms of the slab kick off mechanism can be viewed from remote location in the control panel screen in the electrical control room as shown in Figure 5. This along with other screens as shown in Figure 5 given the amount of skew in mm , the motor speed , motor current and drive healthiness. The operator can control and monitor the movement of the arms of the slab kick off mechanism without causing any damage to the arms due to inadvertent mal-operation. The control panel desk is situated in the electrical control room. The control panel screen shows the animated

movements of the slab kick off mechanism in one of the screen. The second screen shows the skew values as indicated by the absolute encoder (in mm).

Therefore according to one of the aspect of the present invention there is provided a synchronized movement of the two arms of slab kick off mechanism driven by individual motor and coupled to the common slab pushing arm and the said system comprising of: a Programmable Logic Controller(PLC) means installed in the control panel for storing the logic for the synchronized movement of the individual arms of slab kick off mechanism and giving the speed reference to each drive panel of the individual arms of slab kick off mechanism based on the amount of skew between the two arms of slab kick off mechanism; a pair of absolute encoder installed on the output shaft of gear box connected with the individual DC motor configured for sending the position (in counts) of the individual arms of slab kick off mechanism to the Programmable Logic Controller (PLC) through communication cable; a pair of incremental encoder installed on the non-driving end of the motor shaft of the individual motor configured for sending the motor speed (in rpm) to its own DC drive panel; at least one digital drive panels means installed in the control panel for each arm of slab kick off motor, which generates the firing angle for the convertor of that motor based on the speed reference given by the Programmable Logic controller through the communication cable connecting the drive panel to the PLC; a rotary limit switch means installed on the output shaft of gear box of the each arm of slab kick off mechanism for giving the forward and reverse limit position and a control panel including PLC and a plurality of screens installed for real time viewing the amount of skew between the two arms of slab kick off mechanism , motor current , speed and the position of the two arms of slab kick off mechanism from remote location.

Although the foregoing description of the present invention has been shown and described with reference to particular embodiments and applications thereof, it has been presented for purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the particular embodiments and applications disclosed. It will be apparent to those having ordinary skill in the art that a number of changes, modifications, variations, or alterations to the invention as described herein may be made, none of which depart from the spirit or scope of the present invention.

The particular embodiments and applications were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such changes, modifications, variations, and alterations should therefore be seen as being within the scope of the present invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.

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