EP0514402A1 - Tobacco feed system for cigarette making machine. - Google Patents

Abstract

In a tobacco supply system connected to a cigarette production machine, a closed airflow is established in a vacuum belt apparatus (10) by means of a fan (82), said flow passing through a chimney (76) and an air permeable web (84), on which the tobacco layer (86) is formed before being fed to the cigarette production machine. Tobacco particles are drawn into this closed airflow from a hopper (12) through which another open airflow system is established, a single flow connection (72) being provided between the closed airflow (80) and the open airflow system, through which air passes to compensate for leaks from the closed system. This connection can be made by another closed flow system inside which further processing of the tobacco particles takes place, and, in the same way, additional air flow systems can be connected to the system. flow open. These provisions make it possible to eliminate the air locks between the various parts of the system.

Description

Tobacco Feed System for Cigarette Making Machine.

TECHNICAL FIELD This invention relates to a method and device for feeding and conditioning tobacco particles from a source of cut, unopened tobacco to form a continuous tobacco filler on a moving air-permeable suction band in a cigarette making machine.

BACKGROUND ART In the manufacture of cigarettes, tobacco is usually conveyed pneumatically to the cigarette making machine from a central tobacco storage apparatus supplying a number of cigarette making machines. This tobacco feeding system comprises generally a tobacco sender apparatus, part of the central tobacco storage apparatus, which includes a source of cut tobacco and means for feeding tobacco particles into a conveying air stream which conveys the tobacco particles to a hopper apparatus associated with the cigarette making machine. This sender apparatus is generally operated under vacuum. A central fan acting through a vacuum distribution duct is usually the source of the vacuum. An airlock must be used to isolate the subatmospheric pressure existing in the sender apparatus from the ambient atmospheric pressure prevailing in a conventional cigarette making machine hopper. From the airlock the tobacco is discharged into the hopper apparatus. A conventional hopper generally comprises a tobacco storage zone and pre etering, metering and opening devices which condition the tobacco into a wide thin stream of separated tobacco particles before these tobacco particles are entrained by an air stream and conveyed to the air-permeable suction band. Excess tobacco, trimmed from a continuous tobacco layer on the air-permeable suction band, is mechanically conveyed back to the hopper.

The tobacco can be delivered to the cigarette machines intermittently or continuously.

An intermittent tobacco delivery is the most common practice. Each period of delivery fills a discharge device which acts as the airlock. The discharge device then discharges a set amount of the tobacco into the hopper apparatus when the hopper apparatus calls for tobacco.

In a continuous tobacco delivery a rotary airlock continuously discharges tobacco into the hopper apparatus at a rate which is controlled by the hopper apparatus. Depending on the location of the rotary airlock device, the hopper device operates under the ambient atmospheric pressure or under a subatmospheric pressure prevailing in the air stream separated from the tobacco particles received from the sender apparatus. In the latter application the hopper apparatus becomes an integral part of the feeding system.

However, there have been proposals to eliminate the need of an airlock at each cigarette making machine and this invention is more specifically concerned with such systems.

DISCLOSURE OF THE INVENTION I have found that I can eliminate the need for such airlocks without major redesign of either the sender apparatus or the cigarette making machines by operating the hopper under vacuum, and setting up a closed circuit airflow by means of which tobacco particles from the hopper are conveyed to the suction band, this closed circuit airflow being in airflow communication only with the hopper in order to permit leakage into the closed circuit airflow to be removed.

According to the invention, there is provided a method of feeding tobacco to a cigarette making machine comprising conveying premetered and preopened tobacco particles in a first stream of air from a tobacco sender apparatus to a hopper apparatus, disentraining said premetered and preopened tobacco particles from said first air stream, further metering and opening of said disentrained tobacco particles, producing a continuous carpet of said further etered and opened tobacco particles, discharging separated tobacco particles from said continuous carpet through the exit out of the hopper apparatus into a second air stream, entraining and conveying said entrained tobacco particles towards an air-permeable suction band for formation, by withdrawal of the second air stream, of a layer of tobacco particles for conveyance to a tobacco rod forming means of the cigarette making machine, wherein said first air stream is induced by a first fan operating in an open airflow system and said second air stream is induced by a second fan operating in a closed airflow system, wherein the hopper apparatus is operated at the pressure existing in said open airflow system at that location, and wherein said open and closed airflow systems are connected only through said passage, and the pressures in the passage at its points of connection to the air flow systems are substantially equal to the pressures *in the air flow systems at those points so that airflow through said passage between the air flow systems is limited to leakage of said closed system.

The invention also extends to apparatus for feeding tobacco to a cigarette making machine, comprising a tobacco sender apparatus having means for entraining preopened and premetered tobacco particles into a first air stream, a first duct for receiving and conveying said entrained tobacco particles, a hopper apparatus having an entrance for receiving said entrained tobacco particles from the downstream end of said first duct and including means at the entrance to the hopper apparatus for disentraining them from said first air stream, means for further metering and opening said disentrained tobacco particles, means for producing a continuous carpet of said further metered and opened tobacco particles, means for discharging separated tobacco particles from said continuous carpet through an exit out of the hopper apparatus a second duct for receiving said separated particles into a second stream of air, and an air-permeable suction band receiving the separated tobacco particles and forming them into a bed for conveyance to tobacco forming means of the cigarette making machine, wherein said first air stream is induced by a first fan operating in an open airflow system and said second air stream is induced by a second fan operating in a first closed airflow system, wherein said hopper apparatus further comprises an inclosure for the hopper apparatus to maintain it at a subatmospheric pressure existing in said open airflow system at that location, wherein said closed airflow system has a single pressure equalization connection to said open airflow system at the point of entry of tobacco particles from said hopper apparatus, in that additional airflows caused by leakages into said closed airflow system are passed through said pressure equalization connection into said hopper apparatus and withdrawn by said first fan, and wherein said closed airflow system is operating within the environment of said open airflow system.

This invention eliminates the need for an airlock at each cigarette making machine and it also provides following advantages: Since the first air stream which is conveying the tobacco particles from the sender apparatus through the first duct to the hopper apparatus and the second air stream which is conveying the separated tobacco particles through the second duct to the air-permeable suction band, are induced by different sources of the vacuum, the hopper apparatus can be connected without any changes to any conventional type of discontinuous or continuous sender apparatus which is able to supply sufficient tobacco for continuous operation of the cigarette making machine.

The two main functions of the traditional airlock, that is to separate the subatmospheric pressure existing in the system from the atmospheric pressure and to separate tobacco from the conveying air, are performed by the tobacco layer on the continuously moving air-permeable suction band in cooperation with the vacuum existing in the suction conveyor apparatus.

The remaining function is performed by the hopper apparatus, which functions as a magazine of variable tobacco capacity. The tobacco weight per fill of the hopper can vary from zero (in the continuous mode) to the tobacco capacity of the hopper (in the discontinuous mode) . In most instances this feature will allow feeding of a high performance cigarette making machine using presently available feeding systems without changing the diameter of the tobacco conveying duct.

The hopper apparatus can be also connected to any type of cigarette making machine using an air-permeable suction band for formation of a tobacco layer without any changes to the existing stem extraction and tobacco layer formation systems. The fans used for these operations, instead of operating in the ambient atmosphere as is the present practice, operate instead under the pressure conditions established in the hopper apparatus. Since the pressure head of the fan is not dependent on the pressure conditions in the surrounding environment, their settings and operation can be unaffected.

In a preferred arrangement the pressure equalization connection, between the closed airflow system, incorporating the second duct and the suction band, and the hopper, is by means of an intermediate recirculating airflow system within which the stems and heavy particles are separated from the tobacco particles.

Further features of the invention will be apparent from the following description with reference to the attached drawings.

BRIEF DESCRIPTION OF DRAWINGS

Figure 1 is a schematic front view with parts in section and parts removed for clarity of a first embodiment of a system in accordance with the invention;

Figure 2 is a schematic vertical section on the line A-A in Figure l

Figure 3 is a schematic front view, with parts in section and parts removed for clarity, of a second embodiment of a system in accordance with the invention;

Figure 4 is a schematic vertical section on the line A-A in Figure 3;

Figure 5 is a fragmentary vertically transverse sectional detail on line B-B.

Figure 6 is a schematic front view with parts in section and parts removed for clarity of a third embodiment of the system in accordance with the invention; Figure 7 is a schematic vertical section on the line A-A in Figure 6;

Figure 8 is a fragmentary vertically transverse sectional detail on line B-B.

Figure 9 is a fragmentary vertically transverse sectional detail on line C-C.

Figures 10 and 11 are vertically transverse sectional details on the lines D-D and E-E.

Figure 12 is a schematic front view with parts in section and parts removed for clarity of a fourth embodiment of the system in accordance with the invention.

Figure 13 is a schematic vertical section on the line A-A in Figure 12.

BEST MODES OF CARRYING OUT THE INVENTION Referring to the first embodiment of Figures l and 2, the system comprises an air-permeable suction band apparatus 10 associated with a cigarette making machine (not otherwise shown), a hopper apparatus 12, and a sender apparatus not otherwise shown, since the hopper apparatus 12 can be associated with any type of the sender apparatus.

Premetered and preopened tobacco particles 14 are air- conveyed in an air stream 16 through a tobacco duct 18 from the sender apparatus to the hopper apparatus 12. A central fan (not shown) acting through a vacuum distribution duct 20 is the source of the vacuum which induces the air stream 16. The tobacco particles 14 enter the hopper apparatus 12 through a downwardly curved pipe 22 opening into a zone above the level of tobacco contained in a tobacco metering tube 24. The tobacco particles 14 are disentrained in this zone of the tobacco metering tube- 24. The flow of the conveying air 16 fluidizes an upper layer 26 of tobacco in the tobacco metering tube 24 before it is drawn upwardly through a screen 28. This fluidization distributes the tobacco particles 14 evenly in the tobacco metering tube 24. The screen 28 separates the tobacco particles 14 from the conveying air stream 16.

The tobacco metering tube 24 is equipped with a monitoring device 30 which by monitoring the tobacco level regulates the supply of tobacco from the sender apparatus. The tobacco metering tube 24 receives the air-conveyed tobacco particles 14 and thereby provides a tobacco reservoir 32 of premetered and preopened tobacco particles 14 for continuous or discontinuous supply of an adequate amount of tobacco required for formation of a cigarette rod. The tobacco metering tube 24 communicates at its lower end with a housing 34 containing a pair of counter-rotating metering drums 36 and an opening drum 38. The housing 34 communicates also with a trimmed tobacco metering tube 40, which provides a trimmed tobacco reservoir 42 of trimmed tobacco particles 44, as best seen in Figure 1.

The opening drum 38 showers the metered and separated tobacco particles 14 and 44 onto a transport drum 46 at a total flow rate which is equal to the amount of tobacco required for formation of a cigarette rod plus a predetermined tobacco excess to allow for trimmed tobacco particles 44 cut off by a pair of trimmer discs 48 in the suction band apparatus 10 as best seen in Figure 1. The total flow rate is regulated by a monitoring device 50 located at a density equalizer column 52. The monitoring device 50 comprises columns of photocells which monitor the tobacco level in the ^"equalizer column 52 and regulate the speed of the metering drums 36 stepwise in accordance with the number of photocells uncovered by tobacco. The transport drum 46 carries the separated tobacco particles 14 and 44 past a magnet 54 which removes any ferrous metal. The density equalizer column 52, which is evenly filled with the separated tobacco particles 14 and 44, discharges at its lower end a tobacco carpet 56 of uniform density onto an outer surface 58 of a transfer drum 60 as best seen in Figure 2. The outer surface 58 includes a plurality of radial projections 62 for a positive transfer of the continuously moving tobacco carpet 56 through a passage 64 defined between the outer surface 58, left and right sides walls 66 and an arcuate shell 68 which is coaxial with the transfer drum 60. The arcuate shell 68 and left and right side walls 66 are parts of the housing 34 of the hopper apparatus 12. The distributor of the tobacco particles 14 and 44 across the depth of the tobacco carpet 56 correspond to the relative positions of the metering tubes 24 and 40.

A picker roller 70 removes the tobacco carpet 56 from the transfer drum 60 and discharges the separated tobacco particles 14 and 44 into an exit passage 72 at a total flow rate which is equal to the amount of tobacco required for formation of a cigarette rod plus a predetermined tobacco excess to allow .for trimmed tobacco particles 44. The total flow rate is regulated by a monitoring device 74 located at the trimmed tobacco metering tube 40, as best seen in Figure 1.

The discharged and separated tobacco particles 14 and 44 enter through the exit passage 72 and a stem extraction device (not shown) into a chimney 76 are entrained in a second air stream of air 78. The chimney 76 is a part of a closed airflow system 80 where a fan 82 induces the second air stream 78. The entrained tobacco particles 14 and 44 are conveyed through the chimney 76 towards an air-permeable suction band 84, for formation of a tobacco layer 86. The locations of the tobacco particles 14 and 44 within the tobacco layer 86 correspond also with the positions of the metering tubes 24 and 40. The second air stream 78 is then withdrawn through the air-permeable suction band 84 and the tobacco layer 86 into a vacuum chamber 88, part of the air- permeable suction band apparatus 10. The vacuum chamber 88 is divided by a vacuum divider 90 into two zones 92 and 94. The position of the divider 90 is determined by a condition that the amount of the airflow through the upper part of the chimney 76 should approximately equal to the amount of the airflow withdrawn from the first zone 92 by the second fan 82. The necessary vacuum in the second zone 94 is provided by an additional fan 96. The air-permeable suction band 84 conveys the tobacco layer 86 through a duct vacuum seal device 98 to the pair of trimmer discs 48 and finally to a rod forming device (not shown) as best seen in Figure 1. As previously mentioned, the hopper apparatus 12 can be associated with any type of the cigarette making machine which uses an air-permeable suction band for the formation of the tobacco layer.

Referring to Figure 1 the pair of trimmer discs 48 trim off the predetermined amount of the trimmed tobacco particles 44 into a collector 100. The collector 100 feeds the trimmed tobacco particles 44 into a conveying air stream 102 induced by the vacuum existing in the vacuum distribution duct 20. The air stream 102 conveys the trimmed tobacco particles 44 through a trimmed tobacco duct 104 into a separation chamber• 106, where the trimmed tobacco particles 44 are separated from the air stream 102 by a screen 108. From the separation chamber 106 the trimmed tobacco particles 44 are discharged into a rotary airlock 110. A vacuum sensor 112, located in the separation chamber 106, monitors the trimmed tobacco conveying system for possible tobacco blockages, for an unacceptably high pressure loss across the screen 108 and for an unacceptably high leakage of the rotary airlock 110. The rotary airlock 110 discharges the trimmed tobacco particles 44 into the trimmed tobacco metering tube 40, adjacent to the tobacco metering tube 24. A duct 114 maintains the pressures in both metering tubes 24 and 40 at the same level. The width of the trimmed tobacco metering tube 40 is adjustable in order to be able to set a required amount of trimmed tobacco particles 44 cut off by the trimmer discs 48 from the tobacco layer 86. The monitoring device 74 regulates then the amount of trimmed tobacco particles 44 to the required amount by monitoring the tobacco level in the trimmed tobacco metering tube 40 .

Referring to Figures 1 and 2 the conveying velocity in the tobacco duct 18, which connects the sender apparatus to the hopper apparatus 12, is adjusted by the pressure drop across a partly opened butterfly valve 116. The conveying velocity in the trimmed tobacco duct 104 is adjusted by the pressure drop across a partly opened butterfly valve 118, located in a duct 120 which connects the separation chamber 106 with the vacuum distribution duct 20. Since the reservoirs 32 and 42 of the tobacco particles 14 and 44 perform as a barrier, air ducts 122 and 124 connect the upper part of the hopper apparatus 12 with its lower part and maintain the pressures in these areas at the same level. They also divert additional airflows due to the leakages into the closed airflow system 80 or the lower part of the hopper apparatus 12 into the upper part of the hopper apparatus 12 and from there withdrawn by the central fan.

In the event that for some reason the tobacco particles 14, discharged from the tobacco sender apparatus, plugged the entry to the tobacco duct 18, the conveying air stream 16 would be interrupted, causing sudden increase of subatmospheric pressure in the hopper apparatus 12, since there would be no pressure loss across the partly opened butterfly valve 116. To prevent this from happening a vacuum sensor 126, located in the upper part of the hopper apparatus 12, closes the butterfly valve 116 and opens a butterfly valve 128, located at an air duct 130, to bring the subatmospheric pressure in the hopper apparatus 12 to the ambient atmospheric pressure.

Referring to Figure 1 additional valve 132 is needed in order to fill an empty trimmed tobacco metering tube 40 with tobacco. The two way valve 132, inserted in the trimmed tobacco duct 104 and a duct 134 enable the system to fill the trimmed tobacco metering tube 40 from a source of opened tobacco 136.

Referring to the second embodiment of Figures 3, 4 and 5, the system is identical to the system described and shown in Figures 1 and 2 except that an additional closed airflow system is added to the .feeding system. This system allows changing of the sequence of the traditional hopper operations resulting in the following additional advantages:

There will be a better averaging of tobacco layer height during the tobacco layer formation, since the additional tobacco conveying duct will allow the picker roller to be located very close to the air-permeable suction band. Since there is now no stem extraction operation and the air conveying distance is decreased to the minimum, tobacco layer formation is practically performed by a positive mechanical transfer of the tobacco particles from the transfer drum onto the air-permeable suction band.

Since the heavy tobacco particles (stem) and non-ferrous foreign particles are separated from the tobacco particles before they reach the tobacco column, any damage to the pins of the metering drum or picker roller is eliminated.

In this system a column apparatus, comprising the tobacco density equalizer column, transfer drum and picker roller, is associated with the cigarette making machine rather than with the hopper apparatus. The additional tobacco conveying duct will allow a hopper apparatus of one standard width to supply with tobacco a line of cigarette making machines with different widths of their apparatus.

Assembling the tobacco layer over a longer distance will improve control of the tobacco particles during the tobacco layer assembly, since forces of the same magnitude resulting from the pressurized air velocity control a proportionally smaller mass of the landing tobacco particles. Assembly over a longer distance also improves the averaging of the tobacco height. Both improvements ultimately lead to an improved tobacco height consistency. An improved height consistency allows a decrease in the surplus of tobacco allocated for the trimming and therefore tobacco savings can be realized, since there will be less degradation caused by trimming and recycling of trimmed tobacco.

This system allows not only decrease of the height of the cigarette making machine but it also simplifies its maintenance by permitting easy access to all parts of the column and hopper apparatus.

Referring to Figures 3 and 4 the system comprises an air- permeable suction band apparatus 200 and a column apparatus 202 associated with a cigarette making machine (not otherwise shown), a hopper apparatus 204, and a sender apparatus not otherwise shown, since the hopper apparatus 204 can be associated with any type of the sender apparatus.

As in the previous embodiment described and shown in Figures 1 and 2, a metering tube 206 receives from the sender apparatus air-conveyed tobacco particles 208 and thereby provides a tobacco reservoir 210. of the premetered and preopened tobacco particles 208 for continuous or discontinuous supply of an adequate amount of tobacco required for formation of a cigarette rod. The tobacco metering tube 206 communicates at its lower end with housing 212 containing a pair of counter-rotating metering drums 214 and an opening drum 216. The housing 212 communicates also with a trimmed tobacco metering tube 218, which provides a trimmed tobacco reservoir 220 of trimmed tobacco particles 222, as best seen in Figure 3. The opening drum 216 'showers the metered and separated tobacco particles 208 and 222 onto a transport drum 224 at a total flow rate which is equal to the amount of tobacco required for formation of a cigarette rod plus a predetermined tobacco excess to allow for trimmed tobacco 222 cut off by a pair of trimmer discs 226 in the suction band apparatus -200 as best seen in Figure 3. The total flow rate is regulated by a monitoring device 228 located at a density equalizer column 230, parts of the column apparatus 202. The monitoring device 228 comprises columns of photocells which monitor the tobacco level in the equalizer column 230 and regulate the speed of the metering drums 214 stepwise in accordance with the number of photocells uncovered by tobacco.

The transport drum 224 carries the separated tobacco particles 208 and 222 past a magnet 232 which removes any ferrous metal. From the transport drum 224 the separated tobacco particles 208 and 222 are showered onto a belt conveyor 234 which is moving them towards a stem extraction device 236 at a constant speed. The belt conveyor 234 is - provided with a profiled coating of rubber to ensure a positive transfer of tobacco particles 208 and 222 to the stem extraction device 236.

The stem extraction device 236, which is part of a closed airflow system 238, comprises air chambers 240, 242 and a flotation chamber 244. The air chamber 240 is connected to the outlet of a fan 246 by a duct 248. The outlet of the air chamber 240 is provided with a row of closely adjacent rectangular openings 250 which discharge directed air streams in a direction transversely to the trajectory of the tobacco particles 208 and 222 leaving the belt conveyor 234. The intensity of deflecting air streams can be adjusted by a valve 252 so that tobacco particles 208 of a desired size range tobacco particles 208 ^• are deflected around a deflecting roller 254 into a rectangular duct 256. Heavy tobacco particles (stem) and non-ferrous foreign particles are not deflected into the duct 256 and are intercepted by an airflow in a flotation chamber 244. The flotation chamber 244 is also connected through the air chamber 242 and a duct 258 with the outlet of the fan 246. The fan 246 is inducing an air stream 260, which is passing through the flotation chamber 244. Since the velocity of the air stream 260 can be adjusted by a valve 262, the amount of extracted stem can be set to a desired level. The extracted stem is then removed from the flotation chamber 244 by a screw conveyor 264.

The entry into the rectangular duct 256 is also connected through an air chamber 266 and a duct 268 with the outlet of the fan 246. The additional amount of airflow which can be regulated by a valve 270 will set velocity of an air stream 272 in the rectangular duct 256 to the required level.

The stem free tobacco particles 208 and 222 are entrained by the air stream 272 and conveyed through the rectangular duct 256. At the top of this duct the flow of tobacco particles 208 and 222 is evenly divided into a set of ducts 274 of circular cross-section, as best seen in Figure 5. The tobacco particles 208 and 222 are then conveyed through the set of the ducts 274 and enter the column apparatus 202 through a set of downwardly curved rectangular ducts 276 into a zone above the level of tobacco contained in the density equalizer column 230. The tobacco particles 208 and 222 are disentrained in this zone and the air stream 272 is drawn through a screen 278 and a duct 280 into the inlet of the fan 246, parts of the closed airflow system 238. The centrifugal forces which act on the tobacco particles 208 and 222 passing through the curved rectangular ducts 276 will evenly spread the shower of the tobacco particles 208 and 222 across the width of the density equalizer column 230 as best seen in Figure 3 and 4.

Since at the entry into the rectangular duct 256 the closed airflow system 238 is connected with the environment of the hopper apparatus 204, the pressure at that point of the closed airflow system 238 will be equal to the prevailing pressure in the hopper apparatus 204.

The density equalizer column 230 at its lower end discharges a tobacco carpet 282 of uniform density onto an outer surface 284 of a transfer drum 286. The outer surface 284 includes a plurality of radial projections 288 for a positive transfer of the continuously moving carpet 282 through a passage 290 defined between the outer surface 284, left and right sides walls 292 and an arcuate shell 294 which is coaxial with the transfer drum 286. The arcuate shell 294 and left and right sides walls 292 are parts of the cigarette making machine frame as best seen in Figures 3 and 4. Location of the tobacco particles 222 within the tobacco carpet 282 can be varied and corresponds with the arrangement of the ducts 274.

A picker roller 296 removes the tobacco carpet 282 from the transfer drum 286 and discharges the separated tobacco particles 208 and 222 along a second arcuate shell 298, coaxial with the picker roller 296, into a very short chimney 300 at a total rate which is equal to the amount of tobacco required for formation of a cigarette rod plus a predetermined tobacco excess to allow for removal of trimmed tobacco particles 222. As in the previous system a monitoring device 302 regulates then the total flow rate to the predetermined level by monitoring the tobacco level in the trimmed tobacco metering tube 218, as best seen in Figure 3. The region, where the second arcuate shell 298 tangentially merges into a wall of the chimney 300, comprises series of vertically inclined slots 304, defining a plurality of airflow passages. The slots 304, which connect an air chamber 306 with the chimney 300, may be inclined in the direction of the movement of a tobacco layer 308. Since the chimney 300 and air chamber 306 are parts of a closed airflow system 310, where a fan 312 induces an air stream 314, the slots 304 will discharge a plurality of directed air streams 316 which will deflect the tobacco particles 208 and 222 in the direction of the movement of the tobacco layer 308. The deflected tobacco particles 208 and 222 are then entrained in the air streams 316 and conveyed towards an air-permeable suction band 318 for formation of the tobacco layer 308. The location of the tobacco particles 222 within the tobacco layer 308 corresponds with their position in the tobacco carpet 282. The air streams 316 are then withdrawn through the air-permeable suction band 318 and the tobacco layer 308 into a vacuum chamber 320, part of the air-permeable suction band apparatus 200. The vacuum chamber 320 is divided by a divider 322 into two zones 324 and 326. The position of the divider 322 is determined by a condition that the amount of the airflow through the upper part of the chimney 300 is approximately equal to the amount of the airflow withdrawn from the first zone 324 by the fan 312.

At the entry into the chimney 300, the closed airflow system 310 is connected , with the environment of the column apparatus 202 and therefore the pressure at that point of the closed airflow system 310 will be equal to the prevailing pressure in the column apparatus 202. Since the tobacco in the density equalizer column 230 performs as a barrier, a duct 328 connects the upper part of the column apparatus 202 with its lower part and maintains the pressures in these areas at the same level. It also diverts additional airflows due to leakages into the closed airflow system 310 or from the lower part of the column apparatus 202 into its upper part and from there through the fan 246 into the closed airflow system 238. From there these airflows together with additional airflows, this time due to leakages into the closed airflow system 238 or the lower part of the hopper apparatus 204, are diverted through ducts 330 and 332 into the upper part of the hopper apparatus 204 and thence withdrawn by the central fan.

As in the previous system the conveying velocity in a tobacco duct 334, which connects the sender apparatus to the hopper apparatus 204, is adjusted by the pressure drop across a partly opened butterfly valve 336. In the event that for some reason the tobacco particles 208 plug the entry to the tobacco duct 332, a vacuum sensor 338, located in the upper part of the hopper apparatus 204, closes the butterfly valve 336 and opens a butterfly valve 340, to bring the subatmospheric pressure in the hopper apparatus 204 ambient atmospheric pressure, as best seen in Figure 4. The necessary vacuum in the second zone 326 of the vacuum chamber 320 is provided by an additional fan 342. The air- permeable suction band 318 conveys the tobacco layer 308 through a duct vacuum seal device 344 to the pair of trimmer discs 226 and finally to a rod forming device (not shown) as best seen in Figure 3. The handling of the trimmed tobacco particles 222 and adjustment of the velocity in the trimmed tobacco duct are the same as in Figures l and 2.

In the event that for some reason the tobacco particles 208 or 222 plug one of the inlets of the ducts 274, one of tobacco sensors 344, located at these inlets, stops the metering drums 214 and the transfer drum 286 to prevent plugging of the rectangular duct 276, as best seen in Figure 5.

Referring to the third embodiment shown in Figures 6-11, this system is identical to the previous system described and shown in Figures 3-5 except that it permits variation of the rate of tobacco supply to the suction band along the short chimney. This system has the following advantages:

A significantly higher rate of tobacco supply to the suction band at the beginning of tobacco layer formation makes economical use of available vacuum, whilst a significantly lower rate of delivery of well separated tobacco particles during the final stages of tobacco layer assembly will improve the height consistency of the layer. This will lead to tobacco savings through reduced tobacco degradation due to less tobacco being trimmed off.

A significantly lower rate of tobacco supply in the final stages of tobacco layer formation also allows increasing the velocity of the suction band without any effect on the quality of the tobacco layer, since forces of the same magnitude due to velocity and pressure drop across the layer will control a significantly smaller mass of landing tobacco particles. Increased production speed leads to savings in production cost.

The performance of the hopper can be comparable with a conventionally operated hopper of greatly increased width. This embodiment can provide a solution for increasing the performance of existing hoppers, since there is always a practical design limitation upon hopper width and also a practical limit to the magnitude of the vacuum in the suction conveyor.

The system comprises an air-permeable suction band apparatus 400 and a column apparatus 402 associated with a cigarette making machine (not otherwise shown) , a hopper apparatus 404, and a sender apparatus not otherwise shown, since the hopper apparatus 404 can be associated with any type of sender apparatus. As in previous systems shown and described in Figures 1-2 and Figures 3-5, a metering tube 406 receives from the sender apparatus air-conveyed tobacco particles 408 and thereby provides a tobacco reservoir 410 of premetered and preopened tobacco particles 408 for continuous or discontinuous supply of an adequate amount of tobacco required for formation of a cigarette rod. The metering tube 406 communicates at its lower end with housing 412 containing a pair of counter-rotating metering drums 414 and an opening drum 416. The housing 412 communicates also with a trimmed tobacco metering tube 418, which provides a trimmed tobacco reservoir 420 of trimmed tobacco particles

,422, as best seen in Figure 6. The opening drum 416 showers the metered and separated tobacco particles 408 and 422 onto a belt conveyor 424 at a total flow rate which is equal to the amount of tobacco required for formation of a cigarette rod plus a predetermined tobacco excess -to allow for trimming of tobacco particles 422. The flow rate is regulated by a monitoring device 426 located at a first density equalizer column 428, in the column apparatus 402.

The monitoring device 426 comprises columns of -photocells

^' which monitor the tobacco level in the first density equalizer column 428 and regulate the speed of the metering drums 414 stepwise in accordance with the number of photocells uncovered by tobacco, as best seen in Figures 9 and 11.

Referring to Figures 8-11, the stem free tobacco particles 408 and 422 are entrained by an air stream 430, conveyed through a rectangular duct 432 at the top of which the flow of the tobacco particles 408 and 422 is evenly split into a set of ducts 434 of circular cross-section as best seen in Figure 8. The tobacco particles 408 and 422 are then conveyed through the set of ducts 434 and enter the column apparatus 402 through a set of downwardly curved rectangular ducts 436 into two zones above the level of tobacco contained in the first density equalizer column 428 and a second density equalizer column 438. The tobacco particles 408 and 422 are disentrained in these zones of the columns 428 and 438. The air stream 430 is drawn through a screen 440 and a duct 442 into an inlet of a fan 444, forming parts of a closed airflow system 446. The centrifugal forces which act on the tobacco particles 408 and 422 passing through curved ducts 436 will evenly spread the shower of the tobacco particles 408 and 422 across the width of the density equalizer columns 428 and 438, as best seen in Figure 7 and 9.

The density equalizer columns 428 and 438 at their lower ends discharge the tobacco particles 408 and 422 to form two tobacco carpets 448 and 450 of uniform densities onto outer surfaces of two coaxial transfer drums 452 and 454. Two coaxial picker rollers 456 and 458 remove the tobacco carpets 448 and 450 from transfer drums 452 and 454 and discharge the separated tobacco particles 408 and 422 along arcuate walls 460 and 462 into a chimney 464, at a total flow rate which is equal to the amount of tobacco required for formation of a cigarette rod plus a predetermined excess to allow for the tobacco 422 removed by trimming. As in the system shown and described in Figures 1 and 2, a monitoring device 466 regulates then the total flow rate to the required level by monitoring the tobacco level in the trimmed tobacco metering tube 418 as best seen in Figure 6. It should be noted that the speeds of the transfer drums 452 and 454 are different and are proportional to the required intensities of the tobacco supply to the air-permeable suction band 470.

The tobacco particles 408 and 422 are then entrained in air streams 468 and conveyed through the chimney 464 towards an air-permeable suction band 470 for formation of a tobacco layer 472. The air streams 468 are induced by a fan 474, which is part of an closed airflow system 476. Location of the tobacco particles 422 within the carpets 450 and 448 and within the tobacco layer 472 can be also varied and corresponds with the positional arrangement of the ducts 434, as best seen in Figures 6 and 7.

T_he discharge flow rate of the tobacco particles 408 and 422 from the second density equalizer column 438 is also regulated by a monitoring device 478. The monitoring device 478 comprises columns of photocells which monitor the tobacco level in the second density equalizer column 438 and increases or decreases the speed of the transfer drum 454 in relation to the transfer drum 452 stepwise in accordance with the number of photocells uncovered by tobacco. The picker rollers 456 and 458 have also separate drives to allow for different tobacco opening quality of tobacco particles 408 and 422 during the final stages or at the beginning of the tobacco layer assembly, as best seen in Figures 10 and 11.

In the event that for some reason the tobacco particles 408 or 422 plug the entry into a stem extraction device 480 a tobacco sensor 482 stops the metering drums 414 and the cigarette making machine, as best seen in Figure 7.

The air-permeable suction band apparatus 400, stem separation, and handling of the trimmed tobacco particles 422 are also conceptually identical to those previously described and shown in Figures 3-5.-

Procedures for adjusting the air-conveying velocities of tobacco particles 408.and 422 are identical to those shown and described in Figures 1 and 2.

Referring to the fourth embodiment shown in Figures 12 and

13, this is identical to the previous embodiment shown in Figures 6-11 except that the control of the predetermined tobacco excess, to allow for trimmed tobacco removed by trimming, is omitted and the trimmed tobacco is evenly spread over the width of a belt conveyor.

As in the previous embodiment shown and described in Figures 6-11, this embodiment comprises an air-permeable suction band apparatus (not shown) , a column apparatus (not shown) , a hopper apparatus 500, and a sender apparatus not otherwise shown, since the hopper apparatus 500 can be associated with any type of the sender apparatus.

The hopper apparatus comprises in this embodiment only one metering tube 502 which receives air-conveyed tobacco particles 504 and thereby provides a tobacco reservoir 506 for continuous or discontinuous supply of an adequate amount of tobacco required for formation of a cigarette rod. The metering tube 502 communicates at its lower end with housing 508 containing a pair of counter-rotating metering drums 510 and an opening drum 512. The opening drum 512 showers the metered and separated tobacco particles 504 onto a belt conveyor 514 at a flow rate which is equal to the amount of tobacco required for formation of a cigarette rod, as best seen in Figure 13. As in the previous system the flow rate is regulated by a monitoring device (not shown) and located at a first density equalizer column (not shown) . In addition to the tobacco particles 504 the belt conveyor 514 conveys also trimmed tobacco particles 516. A vibrating conveyor 518 showers the trimmed tobacco particles 516 evenly across the belt conveyor 514 at a flow rate which is equal to the predetermined tobacco excess to allow for trimmed tobacco particles 516 cut-off. The belt conveyor 514 discharges the tobacco particles 504 and 516 into a stem extraction device 520 at a total flow rate, which is equal to the amount of tobacco required for formation of a cigarette rod plus a predetermined excess to allow for tobacco 516 removed by trimming. As in the previous system, the stem free particles 504 and 516 are conveyed in an air stream 522 through a rectangular duct 524 and set of ducts (not shown) into the column apparatus (not shown). From-the column apparatus the tobacco particles 504 and 516 are discharged at a total flow rate which is equal to the amount of tobacco required for formation of a cigarette rod plus a predetermined tobacco excess to allow for trimmed tobacco particles 516 cut-off. The flow rate is set manually or it may be regulated by a device (not shown) monitoring the weight of the finished cigarette rod.

As in the system shown and described in Figures 1 and 2 the trimmed tobacco particles 516 are air-conveyed in an air stream 524 through a duct 526 into a separation chamber 528, where they are separated from the air stream 526 by a screen 530. From the separation chamber 528 the trimmed tobacco particles 516 are discharged into a rotary airlock 532. A vacuum sensor 534, located in the separation chamber 528, monitors the trimmed tobacco conveying system for possible tobacco blockages, for an unacceptably high pressure loss across the screen 530 and for an unacceptably high leakage at the rotary airlock 532 The rotary airlock 532 discharges the trimmed tobacco particles 516 onto the vibrating conveyor 518 which, as mentioned above, showers the trimmed tobacco particles 516 onto the belt conveyor 514.

Procedures for adjusting the air-conveying velocities of tobacco particles 504 and 516 are identical to those shown and described in Figures 1 and 2.

The air-permeable suction band apparatus (not shown) and column apparatus (not shown) may be identical to those shown and described in Figures 6-11. The stem separation device 520 may be identical with that shown and described in Figures 3-5. It should be noted that the trimmed tobacco particles 516 are now evenly distributed within the tobacco layer (not shown) .

In a simple modification to the fourth embodiment of the invention, the trimmed tobacco particles are directly spread over the width of the second density equalizer column. This modification has the advantage of reducing degradation of the trimmed tobacco particles because they bypass " the metering, opening and stem extraction operations. Monitoring of the tobacco levels in the first and second density equalizer columns and a subsequent evaluation of the movements of the respective tobacco levels can be used as a feed-back signal for regulating the amount of the trimmed tobacco to the required amount. The trimmed tobacco particles will be evenly distributed but only in the portion of the tobacco layer cross-section which is adjacent to the air-permeable suction band.

It should be noted that the hopper apparatus can permanently operate under atmospheric pressure. In this arrangement the tobacco supply is discharged into the hopper apparatus through an airlock either continuously or discontinuously, or the required amount of tobacco is manually directly into the hopper.

Whilst exemplary embodiments of the invention have been. described, it will be appreciated that, where alternative techniques of performing a given function have been disclosed, these are in many instances interchangeable.

INDUSTRIAL APPLICABILITY Operation of the apparatus described above will now be summarized.

Referring to the embodiment in Figures 1-2, under normal production condition the butterfly valves 116, 118 and 132 are open and the butterfly valve 128. is closed. If the tobacco feed system delivers tobacco to the cigarette making machine continuously, the butterfly valve 116 is open. The vacuum created by the central fan (not shown) induces the air stream 16 in which the tobacco particles 14, discharged_. from the sender apparatus (not shown) , are entrained and conveyed through the tobacco duct 18 into the tobacco metering tube 24 of the hopper apparatus 12. The rate of the discharge of the tobacco particles 14 is regulated by the monitoring device 30. As a result the tobacco level in the tobacco metering tube 24 oscillates around a predetermined level. If the tobacco system delivers tobacco to the cigarette making machine discontinuously, the monitoring device 30 sends a signal to the logic device (not shown) of the tobacco sender apparatus when the tobacco level in the tobacco metering tube 24 drops to a predetermined level. When the tobacco sender apparatus is available for the tobacco delivery, the logic unit simultaneously opens the butterfly valve 116, closes the butterfly valve 128 and starts discharge of the tobacco particles 14 into the air stream 16, which conveys them through the tobacco duct 18 into the tobacco metering tube 24. When the allocated feeding time elapses, the logic unit stops first the discharge of the tobacco particles 14 and after a suitable purge interval has elapsed (so as to empty the tobacco duct. 18 of the tobacco particles 14) it closes the butterfly valve 116 and opens the butterfly valve 128. The system is then ready for a following operation, when the tobacco level in the tobacco metering tube 24 again drops to the predetermined level.

From the metering tubes 24 and 40 the metered and opened tobacco particles 14 and 44 are showered onto the transport drum 46, carried past the magnet 54 which removes any ferrous metal, and subsequently fed into the density equalizer column 52. The feeding rate of tobacco particles from tubes 24 and 40 is regulated by the monitoring device 50 which controls the tobacco level in the density equalizer column 52. The density equalizer column 52 discharges the uniform tobacco carpet 56 onto .the transfer drum 60. The picker roller 70 then discharges the separated tobacco particles 14 and 44 of the tobacco carpet 56 through the exit passage 72 and the stem extraction device (not shown) into the second air stream 78. The discharging rate of tobacco particles 24 and 40 is regulated by the monitoring device 74 which controls the tobacco level in the trimmed tobacco metering tube 40. The stem free tobacco particles 14 and 44 are conveyed through the chimney 76, which is part of the closed airflow system 80, onto the air-permeable suction band 84, which then conveys a layer 86 of the accumulated tobacco particles 14 and 44 from the top of the chimney 76 through the duct vacuum seal device 98, past the pair of the trimmer discs 48, and into the rod forming device (not shown) of the cigarette making machine. The trimmed tobacco particles 44 are fed into the conveying air stream 102 and conveyed through the trimmed tobacco duct 104 to the rotary airlock 110 which discharges the trimmed tobacco particles 44 into the trimmed tobacco metering tube 40, part of the hopper apparatus 12.

During the cigarette making machine start-up, the cigarette making machine opens the butterfly valve 118, if it was not previously open, which stays permanently open until the cigarette making machine is shut-off or a trimmed tobacco blockage occurs in the trimmed tobacco return system. If the tobacco feed system delivers tobacco to cigarette making machine continuously, the monitoring device 30 simultaneously opens the butterfly valve 116, closes the butterfly valve 128 and starts the discharge of the tobacco particles 14 from the tobacco sender apparatus into the air stream 16. The system then operates under normal production conditions.

If the cigarette making machine, including the moving parts of the hopper apparatus 12, stops for any reason and the tobacco feed system is arranged to deliver tobacco to the cigarette making machine continuously, the monitoring device 30 detects a rise in the tobacco level in the tobacco metering tube 24 and interrupts the discharge of tobacco particles 14 from the sender apparatus into the conveying air stream 16. When a suitable purge interval has elapsed (so as to empty the tobacco duct 18 of tobacco particles 14) then the butterfly valve 116 closes and the butterfly valve 128 opens. The system is then ready for restarting of the cigarette making machine.

In the event that the tobacco particles 14, discharged from the tobacco sender apparatus, have for some reason plugged the entry of the tobacco duct 18, the vacuum sensor 126 simultaneously interrupts the discharge of the tobacco particles 14 from the sender apparatus, closes the butterfly valve 116, opens the butterfly valve 128 and stops the cigarette making machine. When the tobacco blockage is removed and the system is ready for operation, a logic unit starts the system commencing with the purge interval. When the purge interval has elapsed the system is ready for start-up of the cigarette making machine.

An unacceptably high pressure loss across the screen 28 or an unacceptably high leakage of air from the atmosphere into the system will decrease the subatmospheric pressure in the hopper apparatus 12. The velocity of the conveying air- stream 16 may not then reach -the required velocity for safe conveyance of the tobacco particles 14. Thus when the vacuum in the hopper .apparatus 12 decreases to a critical level, the vacuum sensor 126 simultaneously interrupts the discharge of the tobacco particles 14 from the sender apparatus and stops the cigarette making machine. When the purge time elapses, the butterfly valve 116 closes and the butterfly valve 128 opens. Upon re-establishing the vacuum, the system is ready for restarting the cigarette making machine. In the event that trimmed tobacco particles 44 plug the entry into the trimmed tobacco duct 104, then the vacuum sensor 112 simultaneously closes the butterfly valve 118 and stops the cigarette making machine. When the trimmed tobacco blockage is removed, the system is ready for start¬ up of the cigarette making machine.

An unacceptably high pressure loss across the screen 108 or an unacceptably high leakage of the rotary airlock 110 will decrease the subatmospheric pressure in the separation chamber 106. The velocity of the conveying air stream 102 may not then reach the required velocity for safe conveying of the trimmed tobacco particles 44, and thus when the vacuum in the separating chamber 106 decreases to a critical level, the vacuum sensor 112 stops the cigarette making machine. When the cigarette making machine comes to a full stop (so as to empty the trimmed tobacco duct 104 from trimmed tobacco particles 44) , the butterfly valve 118 closes. Upon re-establishing the vacuum in the trimmed tobacco return system, the system is ready for the restarting the cigarette making machine.

To fill the empty trimmed tobacco metering tube 40 with tobacco, the monitoring device 74, which is set in the manual mode, simultaneously opens the butterfly valve 118 and two way valve 132. The induced air stream 102 entrains tobacco particles from the source of opened tobacco 136 and conveys them through the duct 134, two way valve 132 and duct 104 into the trimmed tobacco metering tube 40. When the tobacco level reaches the nominal level the monitoring device 74 resets the two way valve 132 to its normally open position and the system is ready for starting the cigarette making machine.

In the event that one of the tobacco levels in the metering tubes 24 and 40 reaches the maximum level or recedes to the minimum level then one of the corresponding monitoring devices 30 or 74 stops the cigarette making machine. Upon re-establishing of the tobacco level in the metering tube 24 or 40, the system is ready-for the restarting the cigarette making machine.

The embodiment shown in Figures 3-5 operates similarly as the embodiment shown in Figures 1-2 except that the stem extraction operation is performed before the tobacco particles 208 and 222 enter the density equalizer column 230. The stem extraction device 236 is now located within the additional closed airflow system 238, which connects the hopper apparatus 204 with the column apparatus 202.

If for some reason the tobacco particles 208 or 222 plug one of the inlets of the ducts 274 which are now parts of the closed airflow system 238, one of tobacco sensors 334 stops simultaneously the metering drums 214, the fan 246 and the cigarette making machine. When the tobacco blockage is removed and the airflow through the closed airflow system 238 is reestablished, the system is ready for start-up of the cigarette making machine.

The embodiment shown in Figures 6-11 operates similarly as the embodiment shown in Figures 3-5 except that the single density equalizer column 230 in the Figure 3 is substituted by two density equalizer columns 428 and 438 in Figure 6. This configuration permits the rate of tobacco supply to the suction band 470 to be varied along the chimney 464.

The total feeding rate of tobacco particles 408 and 422 into the first and second density equalizer columns 428 and 438 is regulated by the monitoring device 426 which controls the tobacco level in the first density equalizer column 428. The total discharge rate of the tobacco particles 408 and 422 into the chimney 464 is regulated by the monitoring device 466 which controls the tobacco level .in the trimmed tobacco metering tube 418. The possibility of imbalance in the magnitudes of the above mentioned tobacco flow rates is avoided by the monitoring device 478 which by controlling the tobacco level in the second density equalizing column 438, increases or decreases the speed of the transfer drum 454 in relation to the speed of the transfer drum 452.

In the event that the tobacco particles 408 and 422 plug ^"the entry into the stem extraction device 480 a tobacco sensor 482 stops the metering drums 414 and the cigarette machine. When the tobacco blockage is removed the system is ready for start-up of the cigarette making machine.

The embodiment shown in Figures 12-13 operates similarly to the embodiment shown in Figures 6-11 except that the trimmed tobacco metering tube 418 with its monitoring device 466, shown in Figure 6, is eliminated. The total discharge rate of the tobacco particles 504 and 516 is set manually or it may be regulated by a device (not shown) monitoring the weight of the finished cigarette rod. The trimmed tobacco particles 516 are discharged from the rotary airlock 532 onto the vibrating conveyer 518 which the distributes them evenly across the belt conveyor 514.

Claims

Claims:

1. A method of feeding tobacco to a cigarette making machine comprising conveying preopened and premetered _.tobacco particles in a first air stream from a tobacco sender apparatus to a hopper apparatus, disentraining said premetered and preopened tobacco particles from said first air stream, further metering and opening the disentrained tobacco particles, producing a continuous carpet of said further metered and opened tobacco particles, discharging separated tobacco particles from said continuous carpet through a passage into a second air stream, entraining and conveying said entrained tobacco particles towards an air- permeable suction band for formation, by withdrawal of the second air stream, of a layer of tobacco particles for conveyance to a tobacco rod forming means of the cigarette making machine, characterised in that said first airstrea is induced by a first fan operating in an open airflow system and said second air stream is induced by a second fan operating in a closed airflow system, in that the hopper apparatus is operated at the pressure existing in said open airflow system at that location, and in that said open and closed air flow systems are connected only through said passage, and the pressures in the passage at its points of- connection to the air flow systems are substantially equal to the pressures in the air flow systems at those points so that airflow through said passage between the airflow systems is limited to leakage of said closed system.

2. A method according to claim 1, characterised in that the passage comprises one or more further closed airflow systems, the pressures existing in said further airflow system or systems at the points of connection to the first closed air flow system and the open airflow system being substantially equal to the pressure in those air systems at those points. 3. A method according to claim 2, wherein any additional airflow caused by leakages into said additional airflow system or systems is passed into said open airflow system.

4. A method for processing cut tobacco to form a tobacco layer on a continuously moving air-permeable suction band and conveying it to tobacco rod forming means of a cigarette making machine, characterised in that it comprises the sequential steps of: feeding unopened cut tobacco into a tobacco sender, located remote from the said cigarette making machine, to provide a source of preopened and premetered tobacco particles suitable for air conveying, entraining tobacco particles discharged from said tobacco sender into a first air stream induced in an open airflow system by a first fan, conveying said first air stream and said entrained tobacco particles from said tobacco sender apparatus through a first tobacco duct of said open airflow system to a tobacco reservoir of a hopper apparatus which is enclosed to maintain a subatmospheric pressure existing in said open airflow system at that location, and disentraining the tobacco particles for residence in said tobacco reservoir, further metering and opening said particles drawn from the bottom of said tobacco reservoir and conveying said tobacco particles into a density equalizer column for producing a density equalized and continuous carpet of tobacco particles, transferring said density equalized carpet of said tobacco particles on the periphery of a transfer drum from said density equalizer column to a picker roller, discharging said tobacco particles from said continuous carpet by said picker roller into a second duct forming part of a closed airflow system for entraining said tobacco particles into an air stream induced in said second duct by a second fan forming part of said closed airflow system; and conveying said second air stream and said tobacco particles through said second duct of said closed airflow system towards an air-permeable suction band for formation a tobacco layer on said suction band by withdrawing said second air stream in said closed airflow system from said tobacco layer to said second fan; only the closed airflow system being connected to the open airflow system along a path followed by tobacco particles passing from the open system to the closed system so that the pressure in the closed system at the point of entry of the particles is ultimately governed by the pressure in the open, system at the point of exit of the particles, said path accommodating leakage in the closed system balancing airflows required by leakage in the closed system.

5. A method according to claim 4, characterised in that the tobacco particles from said sender apparatus form a fluidized bed at the entrance to said hopper apparatus, from which bed the particles are disentrained.

6. A method according to claim 4, characterised in that said tobacco particles are conveyed into said density equalizer column by a transport drum.

7. A method according to claim 4, characterised in that said picker roller discharges said tobacco particles through a stem extraction device into said second duct and wherein said stem extraction device separates stems and non-ferrous foreign particles from said tobacco particles.

8. A method according to claims 4 or 5, characterised in that said tobacco particles are conveyed into said density equalizer column by discharging them through a stem extraction device into an additional air stream induced in an additional closed airflow system by an additional fan. 9. A method according to claim 8, characterised in that said additional air stream and said tobacco particles are split in equal portions and conveyed through a set of ducts of- said additional closed airflow system into a column apparatus, and wherein said column apparatus is enclosed to maintain it at the pressure existing in said additional closed airflow system at that location.

10. A method according to claims 8 or 9, characterised in that said equal portions of said tobacco particles are evenly distributed across the width of the density equalizer column within said column apparatus.

11. A method according to claim 4, 5, 8 or 9, characterised in that said density equalizer column is divided into two compartments and predetermined portions of said tobacco particles are evenly distributed across the width of each of said two compartments for producing two density equalized carpets.

12. A method according to claim 11, characterised in that said tobacco flow rates through said two compartments are different and are proportional to the predetermined portions of the tobacco particles supplied to each compartment.

13. A method according to claim 4 or 5, characterised in that said picker- roller discharges said tobacco particles into said second duct for entraining and conveying said tobacco particles towards said air-permeable suction band for formation said tobacco layer, wherein said tobacco particles are conveyed into separate compartments of said density equalizer column at two different flow rates towards said air-permeable suction band, and wherein said rates are proportional to the ratios of said compartment widths and each compartment is supplied with a predetermined proportion of said tobacco particles. 1₄. A method according to any of claims 4-13, characterised in that_.excess tobacco particles are trimmed off by trimmer discs from said tobacco layer formed on the air-permeable suction band and are discharged into an air stream induced in an additional open airflow system by said first fan, said air stream entrains and conveys said trimmed tobacco particles to a separation chamber for separation of said trimmed tobacco particles from said air stream and for discharging them into a rotary airlock, and wherein said rotary airlock separates the subatmospheric pressure in. said additional open airflow system from fluctuating pressures in said first open airflow system during the discontinuous discharge of said preopened and premetered tobacco particles from said sender apparatus.

15. A method according to claim 14, characterised in that said rotary airlock discharges said trimmed tobacco particles into a trimmed tobacco reservoir for accumulation and subsequent reprocessing, and wherein the required amount of said excess particles is regulated by adjusting the width of said trimmed tobacco reservoir and by monitoring the tobacco level in said trimmed tobacco reservoir.

16. A method according to claim 14 or 15, characterised in that the location of said trimmed tobacco particles within said tobacco layer is controlled by positioning ducts discharging said trimmed tobacco particles into said density equalizer.

17. A method according to claim 14, characterised in that said rotary airlock discharges said trimmed tobacco particles onto a vibrating conveyor for equally spreading them over the width of a belt conveyor conveying particles . forming said carpet of said hopper apparatus within said hopper apparatus. 18. A method according to any of claims 4-17, wherein said premetered and preopened tobacco particles are discharged from said sender apparatus as required to supply a necessary amount of tobacco for continuous running of the cigarette making machine, and wherein the discharge of said particles is controlled by the level of said accumulated tobacco particles in said tobacco reservoir.

19. A method according to any of the preceding claims, characterised in that pressure is monitored at one or more points in the airflow systems to produce one or more signals for controlling valves which operate to relieve abnormal pressure conditions caused by the tobacco plugging a duct or an abnormally high leakage of atmospheric air into the system, and wherein tobacco levels in said hopper apparatus are monitored to produce signals for controlling the rate of tobacco discharge from the hopper.

20. Apparatus for feeding tobacco. to a cigarette making machine, comprising a tobacco sender apparatus having means for entraining preopened and premetered tobacco particles into a first air stream, a first duct for receiving and conveying said entrained tobacco particles, a hopper apparatus having means an entrance for receiving said entrained tobacco particles from the downstream end of said first duct and including means at the entrance to the hopper " apparatus for disentraining them from said first air stream, means for further metering and opening said disentrained tobacco particles, a second duct for receiving and entraining said separated tobacco particles into a second air stream, and an air-permeable suction band of an air- permeable suction band apparatus receiving said separated tobacco particles from the second air stream and forming them into a tobacco layer for conveyance to tobacco rod- forming means of the cigarette making machine, characterised in that said first air stream is induced by a first fan operating in an open airflow system and said second air stream is induced by a second fan operating in a first closed airflow system, in that said hopper apparatus further comprises an enclosure for the hopper apparatus to maintain it at a subatmospheric pressure existing in said open airflow system at that location, wherein said closed airflow system has a single pressure equalization connection to said open airflow system at the point of entry of tobacco particles from said hopper apparatus, in that additional airflows caused by leakages into said closed airflow system are passed though said pressure equalization connection into said hopper apparatus and withdrawn by said first fan, and in that said closed airflow system is operating within the environment of said open airflow system.

21. Apparatus according to claim 20, characterised in that at least one additional closed airflow system is provided between the open airflow system and the closed airflow system, the pressure equalization connection between the open and first closed systems being through at least one additional closed airflow system.

22. Apparatus according to claim 21, characterised in that additional airflows caused by leakages into each said additional closed airflow system are passed directly through - said pressure equalization connection into said open airflow system and withdrawn by said first fan, and wherein each additional closed airflow system is operating within the environment of the airflow system to which its additional airflows are passed.

23. Apparatus according to claim 20, 21 or 22, characterised in that said hopper apparatus comprises a tobacco reservoir defined within said enclosure which has a top entrance portion in which said first duct from said sender apparatus terminates, and which forms a fluidization chamber in which said premetered and preopened tobacco particles separate from said first air stream, two counter rotating metering drums beneath said tobacco reservoir for advancing said tobacco particles therefrom at the required rate, and an opening drum beneath said metering drums for separation of said metered tobacco particles.

24. Apparatus according to claim 23, characterised in that said top entrance portion of said tobacco reservoir comprises a downwardly curved duct forming the down stream end of said first duct from said sender apparatus, oriented to direct said first air stream towards the upper surface of said premetered and preopened tobacco particles accumulated in said tobacco reservoir so that said first air stream penetrates and fluidizes the uppermost portion of said tobacco particles, and a screen above the downstream end of said first duct to separate the first air stream from said tobacco particles.

25. Apparatus according to claim 23 or 24, characterised in that a bypass duct connects the upper and lower part of said hopper apparatus to equalize the pressures in these areas and to direct said additional airflows caused by leakages into the closed airflow system and the lower part of said hopper apparatus to said first fan.

26. Apparatus according to claim 23, 24 or 25, characterised in that it further comprises a transport drum receiving said further metered and separated tobacco particles from the opening drum, a density equalizing column for receiving tobacco particles delivered by the transport drum and for producing a density equalized and continuous carpet, a transfer drum for transferring the continuous carpet from the density equalizing column, and a picker roller for discharging said tobacco particles from said continuous carpet out of said hopper apparatus into said second duct of said closed airflow system for entraining said tobacco particles into said second air stream. 27. Apparatus according to any one of claims 23 to 26, characterised in that stem extraction means are located at the exit of said hopper apparatus for separating stems and non-ferrous foreign particles from the tobacco particles, and wherein said second air stream conveys stem free tobacco particles upwards through said second duct to the continuously moving air-permeable suction band whilst the stems and foreign particles are directed downward through said second duct for collection and removal.

28. Apparatus according to any one of claims 23 to 25, characterised in that said opening drum of said hopper apparatus discharges said separated tobacco particles onto a belt conveyor for conveying them out of said hopper apparatus through a stem extraction device into an additional duct, said additional duct forming part of an additional closed airflow system for receiving and entraining stem free tobacco particles in an additional air stream and conveying them to an divider for dividing an air stream within said additional airflow system and the tobacco particles entrained therein into equal portions, a column apparatus, and a set of ducts for conveying said equal portions into the column apparatus, the column apparatus comprising an enclosure to maintain it at a pressure existing in the additional closed airflow system at that location.

29. Apparatus according to claim 28, characterised in that the stem extraction device is located at the exit of the hopper apparatus for separating stems and non-ferrous foreign particles from the tobacco particles and wherein the extraction device comprises a belt conveyor for establishing a thin carpet of said tobacco particles moving at a predetermined speed, an air chamber issuing through vertical slots a curtain of air and directing it transversely to the trajectory of said tobacco particles leaving said belt conveyor for deflecting upwards a desired size range of said tobacco particles into said additional duct, a flotation chamber for obtaining a required level of stem extraction by adjustment of velocity of an airflow through said flotation chamber, and a screw conveyor for collecting and removal of said stems and foreign particles.

30. Apparatus according to claim 28 or 29, characterised in that the additional closed airflow system further comprises duct means and an additional fan for establishing said additional closed airflow system through said additional duct, said set of ducts, said enclosure of said column apparatus, and wherein said additional closed airflow system has two pressure equalization connections, a first one to said open airflow system at the exit from the hopper apparatus and a second one to said first closed airflow system at the exit from said column apparatus.

31. Apparatus according to claim 28, 29 or 30, characterised in that said column apparatus comprises a top entrance chamber at which said set of ducts terminates, a screen above the termination of the ducts which separates said tobacco particles from said additional air stream, each duct of said set comprising a downwardly curved duct changing its cross-section from circular at an entrance to oblong rectangular at its termination, such that centrifugal forces acting on the tobacco particles along said curved ducts produce directed curtains of the tobacco particles.

32. Apparatus according to claim 31, characterised in that a bypass duct connects upper and lower parts of said column apparatus to maintain the pressures therein at the same level and directs additional airflows caused by leakages into the lower part of said column apparatus and thence through said pressure equalizing connection to the first fan, such that said additional closed airflow system is operating in the pressure environment of the hopper apparatus, regardless of the pressure conditions under which said hopper apparatus operates.

33. Apparatus according to^'claim' 31 or 32, characterised in that said column apparatus further comprises a density equalizing column for receiving said curtains of said tobacco particles and producing a density equalized and continuous carpet, a transfer drum for transferring the continuous carpet from the density equalizing column, and a picker roller, for discharging said tobacco particles from said continuous carpet from the transfer drum out of said column apparatus into the second duct of the first closed airflow system for entraining said tobacco particles into said second air stream.

34. Apparatus according to claim 33, characterised in that the density equalizing column is divided into two compartments, each compartment receiving a predetermined number of said equal portions of said tobacco particles in the form of said curtains, the particles from the two compartments producing two density equalized continuous carpets, and wherein said column apparatus comprises two transfer drums for transferring the two continuous carpets from the two density equalizing compartments to two picker rollers, the two picker rollers discharging the tobacco particles from the two continuous carpets from said column apparatus into said second duct of said closed airflow system for entraining said tobacco particles into said second air stream.

35. Apparatus according to claim 34, characterised in that it includes means to set up flow rates of said tobacco particles through the two compartments which are different and are proportional to the ratio of the number of ducts supplying each compartment with said tobacco particles, and means to drive said two transfer drums at different circumferential speeds proportional to the ratios of the widths of the compartments and the number of ducts supplying each compartment with tobacco particles.

36. Apparatus according to any one of claims 20 to 22, characterised in that the first closed airflow system comprises a second air chamber into which the second airstream issues through vertically inclined slots to entrain said tobacco particles in the direction of said continuously moving suction band, said second duct conveying said entrained and deflected tobacco particles upwards to said air-permeable suction band of said air-permeable suction band apparatus.

37. Apparatus according to any one of claims 20 to 22 and 36, characterised in that said air-permeable suction band apparatus comprises two vacuum chambers, a first vacuum chamber operated at a subatmospheric pressure set up in said first closed airflow system at that location for assembling said tobacco layer on said suction band by withdrawal of said second air stream from said second duct through said tobacco layer and air-permeable suction band into said first vacuum chamber, and a second vacuum chamber operated at a subatmospheric pressure set up in a second open airflow system adjacent said air permeable suction band for conveyance of said tobacco layer on said band from said second duct to said rod-forming means of the cigarette making machine.

38. Apparatus according to claim 37, characterised in that said first closed airflow system comprises duct means for establishing said first closed airflow system through said air chamber, said second duct, said first vacuum chamber and said second fan.

39. Apparatus according to claim 37 or 38, characterised in that said second open airflow system comprises duct means establishing said second open airflow system through said second vacuum chamber and a fan.

40. Apparatus according to any one of claims 20 to 39, characterised in that a pair of trimmer discs is located to trim said excess tobacco particles from said tobacco layer formed on said continuously moving suction band, and a collector of an additional open airflow system is located to collect and entrain said^* trimmed tobacco particles into an air stream induced by said first fan.

41. Apparatus according to claim 40, characterised in that said additional open airflow system comprises a trimmed tobacco duct for continuously conveying said trimmed tobacco particles to a separation chamber for separation said trimmed tobacco particles from said air stream, a rotary airlock for separation of a subatmospheric pressure existing in said second open airflow system at this location from the pressure existing in said first open airflow system at that location and duct means for connecting said separation, chamber with said first fan.

42. Apparatus according claim 41, characterised in that said rotary airlock discharges said separated trimmed tobacco particles into a trimmed tobacco reservoir for accumulating and subsequent reprocessing, wherein a common wall separates said tobacco and trimmed tobacco reservoir, wherein said wall is movable so as to provide a required proportion of said trimmed tobacco particles, and wherein a monitoring device regulates the amount of said tobacco particles to said required- proportion by monitoring the level of said tobacco particles accumulated in said trimmed tobacco reservoir.

43. Apparatus according to claim 41 or 42, characterised in that the location of said trimmed particles within said tobacco layer is controlled by the disposition of ducts through which the tobacco particles are conveyed between the hopper and the air permeable band.

44. Apparatus according to any one of claims 40 to 43, characterised in that it comprises an additional source of trimmed tobacco, and a two way valve operable to permit the filling of said trimmed tobacco reservoir with open tobacco from said addition source in place of said collector.

45. Apparatus according to 41, characterised in that the hopper comprises a vibratory conveyor and a belt conveyor, and in that said rotary airlock discharges said separated trimmed tobacco particles onto the vibrating conveyor, which is located to spread the particles over the width of said belt conveyor , which conveys said further metered and opened particles to said second duct.

46. Apparatus according to any one of claims 20 to 22, characterised in that it comprises at least one additional bypass airflow duct, and means disposed to open said duct in abnormal pressure conditions caused by blockages or excessive leakage of atmospheric air into the apparatus.

47. Apparatus according to claim 46, characterised in that the means to open said of at least one bypass duct is at least one valve controlled by a vacuum sensor.

48. Apparatus according to any one of claims 20 to 47, characterised in that the rate of tobacco discharge into the hopper apparatus is controlled by means sensing the level of accumulated tobacco in the hopper apparatus.

49. Apparatus according to any one of claims 26 or 28 to 35, characterised in that the rate of tobacco discharge into said column is controlled by means sensing the level of accumulated tobacco in the column.