Claims:1. A PLC or microprocessor based system to prevent freely falling object from lifting equipment, the system comprising:
? a rope wire
? at least one rope drum with rope groove and end side metallic circular plates rigidly fixed to support the cylindrical drum
? motors with gear system operatively connected to rope drums to drive the rope drums
? a ferrous magnetic sensor for sensing the drum movement, the sensor mounted in proximity to the end side metallic circular plates of rope drum fixed rigidly from outside facing either a hole or a metal
? Programmable Logic Controllers (PLCs) connected to various components of load lifting equipment to control the operations of the lifting system components
? static brakes to hold the brake drums firmly to stop or resist the free fall till it is fully standstill, wherein
? the ferrous magnetic sensor, senses the hole or metal plate and send output electrical pulses to the PLC and if speed calculated exceeds a pre-defined speed, the PLC sends signal to de-activate the brakes, which holds the brake drums firmly to stop or resist the free fall till it is fully standstill thus protecting the free fall.

2. The system as claimed in claim 1, wherein the side walls of rope drum provided with holes for strengthening and thermal expansion.
3. The system as claimed in claim 1, wherein the ferrous magnetic sensor installed for sensing the hole or metal plate is non contact type and free from maintenance.
4. The system as claimed in claim 1, wherein the ferrous magnetic sensor senses the metal or hole or metallic targets in the rope drum side plate to generate electrical pulses which in PLC calculate the speed of rope drum.
5. The system as claimed in claim 1, wherein the pulse generator is a ferrous magnetic sensor or a photo sensors or any other combination thereof to sense the presence of metal and hole of rope drum and finally process in PLC to calculate speed.
6. The system as claimed in claim 1, wherein ferrous magnetic sensor is an electronic device and does not contain any moving part.
7. The system as claimed in claim 1, wherein the Programmable Logic Controllers (PLCs) generates output when high speed of rope drum is sensed and stops the whole control system and protects the free falling load of lifting equipments by actuating the static brake.
8. The system as claimed in claim 6, wherein the Output from the ferrous magnetic sensor are electrical pulses which are processed in logic circuit prepared in the ladder diagram form.
9. A method to prevent free fall of load from load lifting equipments, the method comprising:
sensing the holes (non-metal) and plate (metal) in rope drum side wall through ferrous magnetic sensor and sending the electrical pulses to PLC for speed calculation which in turn send the signal to de-activate the brakes if rope drum speed calculated as such exceeds a pre-defined speed limit,
generating the “stop” command to switch off control and de-energize the whole control circuit activating the static brakes to hold the brake drums firmly to stop or resist the free fall till it is fully standstill thus protecting the free fall.

10. The method as claimed in claim 9, wherein the ferrous magnetic sensor senses the rope drum speed by means of generating electrical pulses through rotation of the metallic plate or hole provided in the side plate of rope drum.
11. The method as claimed in claim 9, wherein the output is obtained based on the logic circuit prepared in the ladder diagram form.
12. The method as claimed in claim 9, wherein output obtained during high speed sensing in situation of free fall, is used to cut off the brake supply and switch off the total control of this lowering lifting device.
13. The method as claimed in claim 9, wherein output from ferrous magnetic sensor is taken as the input to the existing PLC of crane and is subjected to perform desired logic as per the instructions generated in the circuit.
14. The method as claimed in claim 9, wherein PLC generates an output which de-energies the static brake, holds the brake drum firmly and stops or resists the fall till it is fully standstill when high speed of rope drum is sensed.
15. The method as claimed in claim 9, wherein PLCs are configured to incorporate the pre-defined values according the system requirement.
, Description:Field of invention
The present invention relates to prevent the free falling objects during lifting or lowering operations performed by load lifting equipments like Cranes, hoists, electrical Tackles, CDQ lifters, passenger Lifts etc. The invention more particularly describes PLC based free fall protection system and method for all load lifting equipments. The free fall is prevented by monitoring the speed of rope drum continuously through a control system operable by PLC of load lifting equipments.

Background
The load lifting equipments defined to operate within a certain range of vertical lifting and carrying heavy loads at multi-levels and in multi-directions are known as the crane, hoist and by many other names. In the age of automation, most of the load lifting devices are subjected to work automatic without any operator in the cabin. If the equipments are running in manual mode by operator, he will take care of the free fall cases through using pedal brake from operator cabin as per the requirements and situations. When the operations are automatic, the control system only has to take care of the abnormal situations. When a loaded weight starts falling from height uncontrolled and un-noticed, the situation is very critical and alarming. During such situations this invention plays vital role in protecting the equipments and loads under lifting or lowering. In case of passenger lift, operators do not have brake control but in case of uncontrolled lowering or falling freely, such type of invention will be of great help. Similarly, many heavy load lifting equipments where hundreds of Tons of materials are lifted from remote control room through radio modem or in automatic mode, for those cranes also this type of invention will be a great help. This invention is very much useful for all the load lifting equipments which are operating in automatic mode or semi-automatic mode. For manual lifting operation equipments, this invention will be an additional safety supports for protection of equipments and loads.

The prior art CN103612986B discloses a free fall crane control methods, devices, systems and cranes, the method comprising: obtaining a crane and heavy lifting load of initial rest height, in accordance with crane lifting load determining the height and initial start-up braking stationary heavy weights height; hanging crane load according to correspondence between the braking force setting of braking equipment and braking time to get the maximum allowable weight falling speed, falls below the height of the initial weight of the brake which is not more than the maximum allowable weight falling speed; set according to the braking force of the braking device.

In the prior art, the process of the free-fall crane are checked by a foot brake pedal to operate the brake manually which brakes the spool through the solenoid valve which controls the clutch and the drive separation device, so that the reel and the drive means powered separation. When break drum loosens the brake drum so that heavy objects fall freely under its own weight.

The drawback of the prior art, when the weight drops to the target stop height, the brake pedal to the brake pedal manipulator roll brake, then brake moment will have a greater braking force, the arm rack and wire rope has been badly hit, even cause boom and wire rope breaking, therefore, there is a big security risk. In addition, the existing free-fall crane operation and is suitable for hook load (hook weight) or light load (weight is generally the weight of hook wire rope weight weight<2 tons) free-fall, so that some limitations of the free-fall crane operations exist in the application.

These crane operations are used in various fields. One of such use of lifting machines or crane are used in coke and coal chemical plant in steel plants which produces coke from coal and supplies it to Blast furnaces for iron making. Each coke oven battery having multiple ovens in which coal is charged from top and coal is converted into coke by carbonization process in the absence of air under heating wall of 12500 C temperature. The hot coke thus is pushed out of oven into a coke bucket and carried out by Loco car to another section called Coke Dry Cooling Plant (CDCP). The CDCP section consists of 16 numbers of high speed cranes called CDCP lifters. These cranes have set point of 60-70 Ton weight lifting capacity working round the clock for meeting the cooling target of produced hot coke from battery. The bucket of 25-35Tonweight with 20-40 Ton of hot coke at 10500 C temperature is lifted to a height of 30-40 meters and charged to a closed chamber where coke is cooled down.

Because of frequent operations of lifting and lowering at well side and chamber side, there had been many occasions when output coupling sheared and bucket weight falls from top. The coupling failure or shaft shearing at input side or output side is such a phenomenon when motor power is disconnected from system and bucket is subjected to undergo gravitational pull. Under this condition, bucket falls and severe damages to plant and equipments take place.

Summary of the invention
Free fall incidences of lifting loads through different lifting equipments commonly happen in industries. There are no specific tools to prevent or reduce the damages during such occurrences. The reasons of free fall may be of different kinds i.e. (a) Fall due to snapping of rope (b) due to input drive coupling failure (c) due to output drive coupling failure (d) due to drive torque failure etc. The fall due to rope snapping can be prevented only if proper inspection is done and timely replacement action is taken. In other cases, there are possibilities to eliminate or at least minimize the damages caused due to free fall. Now a days, almost all the cranes are operated through vector drive (VFD) and PLC because of added advantages of new technology. The existing facility of PLC system of crane can be intelligently utilized for free fall prevention of different loads with investment almost nil. All other cases of free fall except rope snapping case can be well protected through proposed technique.

In an embodiment of the present invention, a system to prevent free fall of load from lifting equipment is provided. The system comprises a rope wire rolled on at least one rope drum with rope groove and end side metallic circular plates rigidly fixed to support the cylindrical drum. At least a motor with gear system are connected to rope drums to drive the rope drums. A ferrous magnetic sensor for sensing the drum movement is mounted in proximity to the end side metallic circular plates of rope drum, which is fixed rigidly from outside to either face a hole or a metal. The ferrous magnetic sensor installed for sensing the rotation is non-contact type and free from maintenance. The ferrous magnetic sensor senses the metal or hole or metallic targets in the rope drum side plate to sense the speed of rotation of rope drum. The sensor may be a ferrous magnetic sensor, photo sensor, infrared sensor or any other sensor to sense the metal or no-metal of rope drum. The sensor is an electronic based sensor and does not contain any moving part.

Static brakes to hold the brake drums firmly to stop or resist the free fall till it is fully standstill. The side walls of rope drum provided with holes for strengthening and thermal expansion.

According to further embodiment of the invention Programmable Logic Controllers (PLCs) are provided and connected to various components of load lifting equipment to control the operations of the lifting system components. The Programmable Logic Controllers (PLCs) acts when high electrical pulses are sensed by ferrous magnetic sensor from rope drum rotation and stops the whole control system and protects the free falling load of lifting equipments by actuating static brake.The Output from the speed sensor is obtained based on the logic circuit prepared in the ladder diagram form or any other form.

According to further embodiment the ferrous magnetic sensors senses the electrical pulses, sends pulses to PLC to calculate drum speed and if rope drum speed calculated exceeds a pre-defined speed, the PLC sends signal to de-activate the brakes, which holds the brake drums firmly to stop or resist the free fall till it is fully standstill thus protecting the free fall.
According to another embodiment of invention a method for prevention of free fall of load lifting equipments, the method comprising the steps of:
? sensing the electrical pulses by ferrous magnetic sensor due to drum movement and giving these inputs to PLC for rope drums speed calculation.
? sending the output signal of speed calculated by PLC to de-activate the brakes if rope drum speed exceeds a pre-defined speed limit,
? generating the “stop” command to switch off control and de-energize the whole control circuit
? De-activating the static brakes to hold the brake drums firmly to stop or resist the free fall till it is fully standstill thus protecting the free fall.
The ferrous magnetic sensor senses the presence of metallic plate or hole in the side plate of rope drum when drum rotates during operation and generates electrical pulses.

A ferrous magnetic metallic sensor is mounted near the rope drum to count the holes of drum or metallic targets at the side of drum in one rotation. The maximum speed of lifting or rotating rope drum is known as per crane manufacturer. During free fall, the speed of rotation of rope drum will be higher than the nominal speed of rotation. Hence the basic principle of the ‘protection against free fall’ adopted technique is:

If dn/dt> k then output is high
Whereas k = Set value for normal speed of crane
n = Number of holes or Targets sensed
t = Time taken

The output high is used to energize a relay contact which intern switches off the total control system of lifting device. As the total control is switched off, static brake will come into action to hold the brake drum and ultimately the load will be protected from free fall.

Detailed Description of invention
The rope drum of any lifting device is a hollow cylindrical unit with rope groove to fit into it. From both end sides metallic circular plates are rigidly fixed to support the cylindrical drum. These side walls of rope drum are having plurality of holes for strengthening and thermal expansion. In some cases, if drum is very small for tackle application, the hole in the side drum plate may not be there to take reference. In that case few metallic targets may be fixed to take the reference of speed of rotation. A Ferro metallic sensor is placed near the side wall surface and mounted rigidly from outside to either face hole or metal plate as has been shown in the figure. When rope drum rotates for lifting or lowering, the ferrous magnetic sensor senses the presence of metallic plate or hole. For example, if there are six holes in side rope drum wall hence it senses six times for the presence of metal or hole in one rotation. The sensing speed depends upon the speed of rotation of rope drum designed in combination of motor speed and gear ratio together with number of rope loops to lift the specified load. The size of rope drum is based on the load factor and capacity of the crane or lifting device.

In an exemplary embodiment, the proximity sensor installed for sensing the metal or hole in the rope drum side plate is non-contact type thus free from maintenance. The switching speed is in millisecond and life is more than 10 million operations. This sensor is electronic based and does not contain any moving part hence the reliability is very high and wear and tear is zero. The sensing by this probe is taken as the input to the existing PLC of crane and is subjected to perform desired logic as per instruction of the circuit. The logic control is programmed in PLC and set in the way to function and give desired result.

Output is obtained based on the logic circuit prepared in the ladder diagram form or any other form. The output obtained during high speed sensing which is a situation of free fall, is used to cut off the brake supply and switch off the total control of this lowering lifting device. This new logic circuit de-energies the static brake, holds the brake drum firmly and stops or resists the fall till it is fully standstill. This automatic circuit or programming is a permanent part of the PLC program and acts only when high speed of rope drum is sensed which is set as free fall situation. Its action prevents or minimizes the damages of equipment.

If any ferrous metallic sensor or proximity sensor is already in use, in the system for end cutting purpose or any other purpose but fixed at the same proposed place, we need not to fix another proximity sensor but reference of the same can be used in the programming and it will serve the same purpose without any extra expenditure.

During running, the proximity sensor senses Ferrous (metal plate) and gets ON, again on further rotation it senses non-ferrous (Hole) and gets OFF. This operation continues during rotation of rope drum. The sensing of these two status as presence of ferrous and non-ferrous gives one electrical pulse and it is counted by a counter. If the speed of the drum is high, then the sensing of ferrous and non-ferrous will be also high and more electrical pulses will be counted in defined time period.

A pulse counting duration is decided in view of the speed of rope drum rotation and number of holes passing in front of sensor. The “dt” of the equation is decided based on the actual rope drum movement of the equipment which vary from two seconds to several seconds. The corresponding pulses are recorded and a decision is taken to get a full numerical value which is very close to its maximum speed but sufficient enough not to execute spurious tripping in the equipment. For example, the duration(dt) is taken as 4 second and during this period around 10 - 15 pulses are generated. In view of this, pulse counting (dn) of 16 have been taken set value which will correspond to high speed of rope drum rotation. Hence, dn/dt i.e. pulse recorded per 4 seconds of time duration should be always less than 16 (set value). “K” is constant and basically a ratio of number of pulses sensed per unit time of 4 seconds duration. The value “K” determines the threshold value of normal speed and abnormal speed which is set here as free fall value.

PLC programming in the ladder diagram form is designed with the help of inbuilt feature provided in every PLC. Every PLC of control circuit application will have hundreds of inbuilt timers, counters, comparators, and many more features for different applications in electrical control circuit. For example, a 4 seconds timer is designed with the help of 1second inbuilt timer. This timer is ON for 4 seconds and again it reset to zero. Again it stays for 4 second and reset to zero. This operation continues uninterrupted as long as control is healthy. During this 4 seconds of period, number of pulses are counted and at the end of 4 seconds they are also reset to zero and again new counting starts. This time based counting process continues silently as long as pulse counting are less than 16. The moment counting reaches 16, the “stop” command is generated and that switches off control and de-energize the whole control circuit.

Various PLCs known in the art can be used for the purpose of the present invention and can be programmed to perform the various functions.

The advantages and features of the invention shall be better understood with reference to the following description taken in conjunction with the accompanying drawing, wherein like elements are identified with like symbols and in which The present technique is further described hereinafter with reference to the accompanying drawings, wherein:

Fig 1: is showing a free fall protection system according to present invention
Fig 2: is showing flow diagram of PLC program opted for this technique.
Fig 3: is showing rope drum and sensor mounting.
Fig 4: is showing block diagram for this opted free fall protection.
Fig 5: is showing electrical pulses received during normal operation.
Fig 6: is showing electrical pulses received during free fall conditions.
Fig 7: is showing PLC based ladder logic electrical drawing

For a thorough understanding of the invention, reference is to be made to the following detailed description in connection with the abovementioned drawings. Although the drawings are described in connection with invention, the invention is not intended to be limited to the specific forms set forthherein. It is understood that various omissions and substitutions of equivalents are contemplated as circumstances may suggest or render expedient, but these are intended to cover the application or implementation without departing from true spirit or scope of the invention. Further, it will nevertheless be understood that no limitation in the scope of the invention is thereby intended, such alterations and further modifications in the figures and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. Further, reference herein to "one embodiment" or "an embodiment" means that a particular feature, characteristic, or function described in connection with the embodiment is included in at least one embodiment of the invention. Furthermore, the appearances of such phrase at various places herein are not necessarily all .referring to the same embodiment. The terms "a" and "an" herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.

Fig 1 shows the process flow diagram of hot coke cooling through Nitrogen gas in closed cycle where N2 gas is passed through hot coke of 1050°C temperature and gets heated up to 750°C and further passes through water filled boiler tubes where steam is generated. There is 16 numbers of such sets in CDCP and each set is having 65 ton crane lift hot coke bucket at 34M height with the lifting speed of 0.5m per second. The capacity is 50 times per day per chamber.

Fig 2 shows flow diagram of the adopted free fall protection technique which presents logical sequences how the PLC logic diagram works to meet the required result. The rope drum rotation, its rotation sensing and time counting, all start together. For example, if the counting pulses per four seconds are less than 16 then there is self-resetting and process continue in monitoring state till cranes works. When the pulse counting is more than 16, it immediately interferes and stops the system totally as described above.

Fig 3 shows the schematic diagram of rope drum with proximity sensor fixed for sensing the pulses when rope drum rotates while lifting or lowering the load. As shown, the positioning of proximity switch is just 7mm away from side vertical plate of rope drum and fixed rigidly on separate stand independently from rope drum. As there is no direct contact of proximity switch with rotating drum, the life of proximity switch is very high.

Fig 4 shows the creation of time period of 4 second duration and subsequently number of pulses sensed for ferrous plate and non-ferrous holes coming in front of during this 4 second period. When K>14, Stop command will activate a control relay which will stop the total system. Time taken 4 sec is typical for this case.

Fig 5 shows the actual electrical pulses bar graph received during 4 second duration which is designed as time period for pulse sensing. During the normal operation, for this selected time period, the pulses sensed are always less than 14. This electrical pulse pattern is for normal operation. K=14, set value for pulse counter.

Fig 6 shows the actual electrical pulses bar graph received during 4 second duration which is designed as time period for pulse sensing. During the abnormal operation, for this selected time period, the pulses sensed are always more than 14. This electrical pulse pattern is for abnormal operation.

Fig 7 shows the PLC based small ladder logic program in line with Yaskawa PLC which executes the functioning of free fall protection technique for all the load lifting equipments. The diagram shows that the selected timer block of 1 second time starts functioning when control contact is switched on. This timer is set for 4 second duration and the moment 4 seconds are over, the output relay 001 becomes high and 002 becomes low. This 001 output relay opens the reset contact and stored 4 seconds time becomes zero. The moment timer is reset to zero, output drops and timer starts to function as fresh and timing activities continues. During this 4 second period, 002 output remains high and allows counter 4002 to receive all the pulses coming out of rope drum rotations. At the end of 4 second again this counter gets reset and its content becomes zero. This action continues as long as control is switched on and drums are rotating. The setting and again resetting of timer and counter are continuous and always active. As long as counter 4002 counting reaches 14 and above before it is reset, it means abnormal fast lowering is taking place and in such condition output 003 gets high and subsequently relay 004 stops the whole control system and protects the free falling load of lifting equipments through actuating static brake.

The present invention can be used in all load lifting devices/Machines/cranes. The PLC based programming is only a few rungs as a part of the total program which will be working silently and will act when abnormal speed develops during free fall cases of coupling failure, shaft shearing etc. The contactless proximity sensor provided is maintenance free and highly reliable. This offered technique uses mainly available resources of the system and extra expenditure is almost nil. This technique is PLC based programming and hence physical maintenance is nil. An alarm can be generated in HMI to inform operator about the reason of stoppage of equipment when it operates. Almost all makes PLCs are having the facilities to incorporate the proposed programming in their own methodology.

The foregoing descriptions of specific embodiments of the invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and its practical, application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is understood that various omission and substitutions of equivalents are contemplated as circumstance may suggest or render expedient, but such are intended to cover the application or implementation without departing from the spirit or scope of the invention.